Nanocomposite battery electrode particles with changing properties

ABSTRACT

Battery electrode compositions and methods of fabrication are provided that utilize composite particles. Each of the composite particles may comprise, for example, a high-capacity active material and a porous, electrically-conductive scaffolding matrix material. The active material may store and release ions during battery operation, and may exhibit (i) a specific capacity of at least 220 mAh/g as a cathode active material or (ii) a specific capacity of at least 400 mAh/g as an anode active material. The active material may be disposed in the pores of the scaffolding matrix material. According to various designs, each composite particle may exhibit at least one material property that changes from the center to the perimeter of the scaffolding matrix material.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application for patent is a Continuation of U.S. patentapplication Ser. No. 14/882,166, entitled “Nanocomposite BatteryElectrode Particles with Changing Properties”, filed Oct. 13, 2015,which claims the benefit of U.S. Provisional Application No. 62/063,493,entitled “Nanocomposite Battery Electrode Particles with PropertiesChanging Along their Radii,” filed Oct. 14, 2014, each of which isexpressly incorporated herein by reference in its entirety.

BACKGROUND Field

The present disclosure relates generally to energy storage devices, andmore particularly to battery technologies that utilize powder-basedelectrodes and the like.

Background

Electrochemical energy storage technologies are useful for a broad rangeof important applications, such as energy efficient industrialequipment, electric and hybrid electric vehicles (including groundvehicles, air vehicles, and ships), the electric grid, and consumerelectronics, to name a few. Owing in part to their relatively highenergy densities, light weight, and potential for long lifetimes,advanced metal-ion batteries, such as lithium-ion (Li-ion) batteries,now dominate consumer electronics and electric vehicle applications.However, further development and improvement of various types ofbatteries is needed.

Energy density (energy storage ability per unit volume) is one area forimprovement. The majority of rechargeable batteries utilize electrodescomprising powders of battery materials. These powders exhibitelectrochemical reactions during battery charging or discharging.Unfortunately, materials that offer high volumetric capacity (highion-storage ability per unit volume) to such powders often suffer fromvolume changes during battery operation, which may result in celldegradation. In addition, many such materials additionally suffer fromlow conductivity (at least during some stage of charge or discharge),which may result in low power performance. For example, in the case ofrechargeable metal and metal-ion batteries (such as Li-ion batteries),materials that offer high capacity, such as conversion-type cathodematerials (e.g., fluorides, chlorides, bromides, sulfides, sulfur,selenides, selenium, oxides, nitrides, phosphides and hydrides, andothers for Li-ion batteries), conversion and alloying-type anodematerials (e.g., silicon, germanium, tin, lead, antimony, magnesium,aluminum, their oxides nitrides, phosphides and hydrides, and others forLi-ion batteries) and others, suffer from at least some of suchlimitations. The volume changes during ion (e.g. metal-ion)insertion/extraction, which may cause mechanical and electricaldegradation in the electrodes and (particularly in the case of anodematerials for metal-ion batteries) degradation in the solid-electrolyteinterphase (SEI) during battery operation. This, in turn, typicallyleads to cell degradation. Some of these materials additionally sufferfrom undesirable reactions between the active material and electrolyte(such as dissolution of the active material or the intermediate reactionproduct in the battery electrolyte). This may also lead to celldegradation.

There remains a need for further improved batteries, components, andrelated materials and manufacturing processes for use in various batterychemistries, including but not limited to rechargeable Li and Li-ionbatteries.

SUMMARY

Embodiments disclosed herein address the above stated needs by providingimproved battery components, improved batteries made therefrom, andmethods of making and using the same.

Battery electrode compositions and methods of fabrication are providedthat utilize composite particles. Each of the composite particles maycomprise, for example, a high-capacity active material and a porous,electrically-conductive scaffolding matrix material. The active materialmay store and release ions during battery operation, and may exhibit (i)a specific capacity of at least 220 mAh/g as a cathode active materialor (ii) a specific capacity of at least 400 mAh/g as an anode activematerial. The active material may be disposed in the pores of thescaffolding matrix material. According to various designs, eachcomposite particle may exhibit at least one material property thatchanges from the center to the perimeter of the scaffolding matrixmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are presented to aid in the description ofembodiments of the invention and are provided solely for illustration ofthe embodiments and not limitation thereof.

FIGS. 1A-1D illustrate example composite particle compositions accordingto certain example embodiments, comprising a scaffolding matrix materialand high-capacity active material confined within the scaffoldingmatrix.

FIGS. 2A-2E illustrate different aspects of example composite particlecompositions according to certain example embodiments, comprising ascaffolding matrix material with a gradient composition and active highcapacity material confined within the scaffolding matrix.

FIGS. 3A-3D illustrate example profiles of selected mechanicalproperties of the scaffolding matrix material (of the composite particlecompositions) according to certain example embodiments.

FIGS. 4A-4D illustrate example profiles of the average concentration ofdefects or functional groups of the scaffolding matrix material alongthe radius of composite particles according to certain exampleembodiments.

FIGS. 5A-5C illustrate example composite particle and scaffolding matrixcompositions according to certain example embodiments, where thescaffolding matrix material changes in average pore size along theparticle radius from the center (core) to the perimeter.

FIGS. 6A-6C illustrate example profiles of the average pore size withinexample scaffolding matrix compositions along the radius of theparticles, according to certain example embodiments.

FIGS. 7A-7C illustrate example profiles of the average pore volumewithin example scaffolding matrix compositions along the radius of theparticles, according to certain example embodiments.

FIGS. 8A-8B illustrate example scaffolding matrix compositions accordingto certain example embodiments, where the scaffolding matrix materialchanges pore orientation along the particle radius from the center(core) to the perimeter.

FIGS. 9A-9D illustrate example compositions of active material confinedwithin a scaffolding matrix according to certain example embodiments,where the active material changes composition along the particle radiusfrom the center (core) to the perimeter.

FIGS. 10A-10C illustrate examples of the profiles for the changes inaverage composition of active material along the particle radius fromthe center (core) to the perimeter according to certain exampleembodiments, where the active material is confined within a scaffoldingmatrix.

FIGS. 11A-11D illustrate examples of the profiles for the changes in theselected mechanical properties of active material (such as hardness inFIGS. 11A and 11B, and modulus in FIGS. 11C and 11D) along the particleradius from the center (core) to the perimeter according to certainexample embodiments, where the active material is confined within ascaffolding matrix.

FIGS. 12A-12B illustrate examples of the profiles for the changes indensity of active material along the particle radius from the center(core) to the perimeter according to certain example embodiments, wherethe active material is confined within a scaffolding matrix.

FIGS. 13A-13B illustrate examples of the profiles for the changes in the(Wa/Wsm) relative weight fraction of active material relative to thescaffolding matrix (or the scaffolding matrix and the rest of thecomposite, including the protective coating and the protective shell oradditional filler material, if present in the composite) along theparticle radius from the center (core) to the perimeter according tocertain example embodiments, where the active material is confinedwithin a scaffolding matrix.

FIGS. 14A-14B illustrate examples of the profiles for the changes in the(Va/Vo) relative volume fraction of active material (relative to thetotal volume of the composite) along the particle radius from the center(core) to the perimeter according to certain example embodiments, wherethe active material is confined within a scaffolding matrix.

FIGS. 15A-15D illustrate example composite particle compositionsaccording to certain example embodiments, comprising a scaffoldingmatrix material and high capacity active material confined within thescaffolding matrix, and a protective shell enclosing the compositeparticles and protecting the active material from unfavorableinteractions with electrolyte solvent or ambient environment.

FIGS. 16A-16D illustrate example composite particle compositionsaccording to certain example embodiments, comprising a scaffoldingmatrix material and active high capacity material confined within thescaffolding matrix (and optionally a protective shell), and having arough or high surface area outer surface.

FIGS. 17A-17C illustrate example composite particle compositionsaccording to certain example embodiments, comprising a scaffoldingmatrix material and high capacity active material confined within thescaffolding matrix and a protective shell, and where conductiveparticles penetrate through the shell layer.

FIGS. 18 and 19 illustrate example battery (e.g., Li-ion battery)building blocks, where two different electrolytes are used for the anodeand cathode, respectively, and where at least one electrolyte is solidand infiltrated into the pores between the individual particles of theelectrode.

FIG. 20 illustrates an example battery (e.g., a Li-ion battery) in whichthe components, materials, methods, and other techniques describedherein, or combinations thereof, may be applied according to variousembodiments.

DETAILED DESCRIPTION

Aspects of the present invention are disclosed in the followingdescription and related drawings directed to specific embodiments of theinvention. The term “embodiments of the invention” does not require thatall embodiments of the invention include the discussed feature,advantage, process, or mode of operation, and alternate embodiments maybe devised without departing from the scope of the invention.Additionally, well-known elements of the invention may not be describedin detail or may be omitted so as not to obscure other, more relevantdetails.

In the description below, several examples are provided in the contextof Li-ion batteries because of the current prevalence and popularity ofLi-ion technology. However, it will be appreciated that such examplesare provided merely to aid in the understanding and illustration of theunderlying techniques, and that these techniques may be similarlyapplied to various other metal-ion batteries (such as Na-ion, Ca-ion,K-ion, Mg-ion, and other metal-ion batteries), various batteries thatemploy different ions for anodes and cathodes, various batteries withsolid electrolytes (including those having two electrolytes—one on theanode and another one on the cathode), various batteries with liquidelectrolytes (for example, with organic electrolytes, with aqueouselectrolytes of various pH, with various liquid electrolytes based onionic liquids, or with various liquid electrolytes comprising a mixtureof various components, including those described above).

It will be also appreciated that some aspects of the present disclosuremay be applicable to other areas as well. One example of such anapplication is catalysis, such as catalyst particles, where the “activematerial” may refer to a catalyst particles and a “scaffolding material”may refer to a catalyst support.

The present disclosure provides for advanced composite powder materialsfor battery electrodes comprising sufficiently electrically-conductive“scaffolding” matrix material having “volume changing,” “high capacity,”and “high melting point” active material incorporated therein. Asuitable fraction of active material in the composite powders rangesfrom around 20 wt. % to around 99 wt. %. The “high capacity” activematerial refers to active materials with a specific material capacity inexcess of around 400 mAh/g in the case of anode materials and in excessof around 220 mAh/g in the case of cathode materials. The majority ofsuch active materials belong to the so-called “conversion” materialfamily, where the chemical structure of the active material changesduring charging and discharging. As used herein, so-called “alloying”type anode materials are considered part of the broader class of“conversion” anode and cathode materials. The “high melting point”active material refers to those active materials that have a meltingpoint in excess of around 250° C. Since conversion-type active materialsmay exhibit different melting points during different levels of chargingor discharging, the “high melting point” discussed above refers to thestate of the material during particle synthesis. The “volume changing”active material refers to active materials that experience more thanapproximately 8 vol. % changes during charging or discharging. Thescaffolding matrix material may exhibit substantially (by at least 50%)smaller capacity or substantially (by at least 50%) smaller energydensity compared to the high capacity active material, when used withinthe voltage (potential) range of the composite electrode operation in acell.

As discussed in more detail below, several advantages over conventionaldesigns may be provided by incorporating “high capacity” and “highmelting point” active material into a preferably solid, electricallyconductive scaffolding material matrix. For example, deposition of theactive material inside a scaffolding matrix (as opposed to surfacedeposition) helps avoid the often undesirable agglomeration ofindividual active material particles. A portion of the scaffoldingmatrix can be left exposed and, therefore, used for the stableattachment of a (polymer) binder or assist in the formation of a stablesolid electrolyte interphase (SEI). A more stable particle-binderinterface or more stable SEI may lead to more stable performance of theelectrode.

In cases when direct contact between the electrolyte and active materialis undesirable (for example, in the case of unfavorable reactions, suchas (at least) partial dissolution of the active material or electrolytedecomposition, etc.), the outer surface area of the scaffolding matrixcan also be used for the deposition of an ionically conductive (andelectrolyte solvent impermeable) outer shell, thereby sealing the activematerial deposited inside the scaffolding matrix and avoiding the oftenundesirable contact of active material with solvent molecules of theelectrolyte.

Similarly, in alternative configurations when direct contact between theelectrolyte and active material is undesirable (for example, such as inconversion or alloying-type high capacity electrode materials for use inLi-ion batteries), the scaffolding material may completely encapsulatethe active material and prevent its direct contact with the electrolyte.In this case, it may be advantageous for the scaffolding material topossess both sufficient ionic and sufficient electrical conductivitiesto permit reasonably fast (for a given application) charging anddischarging. In some configurations, it may be favorable for thescaffolding material to additionally store charge (ions) and be“active,” while exhibiting small volume changes (preferably less thanapproximately 8 vol. %) during charging and discharging.

For cases where the active material undergoes further expansion duringcell operation from the state of the material during particle synthesis,it may be advantageous to provide sufficient pore volume within the“scaffolding material-active material” composite to accommodate fromaround 20 vol. % to around 100 vol. % of such a volume expansion withoutcausing composite particle fractures. If less than 100% of the neededvolume for active material expansion is available within the scaffoldingmaterial, it may be advantageous for the scaffolding material to exhibitmaterial properties that are conducive to elastically or plasticallyaccommodate the remaining volume changes without causing compositeparticle fracture.

It may be similarly advantageous for the scaffolding material to possessa sufficient elastic modulus, mechanical strength, and toughness inorder to avoid fractures and failures during the battery cycling-inducedvolume changes in the high capacity active material.

In cases where the active material does not significantly exceed (e.g.,by more than 8 vol. %) its initial volume during each cycle of celloperation (e.g., when the active material already contains the maximumamount of Li and is used in Li-ion batteries), it may be advantageousfor it to possess few or no additional pores so that the volumetriccapacity of the “scaffolding material-active material” composites ismaximized.

The scaffolding matrix may also be used to electrically connectindividual active (nano)particles, which can be important for higherutilization of the active particles. Furthermore, the scaffolding matrixmay be capable of maintaining such electrical connectivity even in caseswhen the active particles change dimensions during insertion andextraction of ions (during battery operation, such as during chargingand discharging).

It may be advantageous for the scaffolding matrix material (or at leasta portion of the scaffolding matrix material) to form a unibody or asingle solid particle (for example, where the scaffolding matrixmaterial atoms are linked via chemical bonds) within a singlescaffolding matrix material-active material composite particle (asopposed to a weak agglomeration of individual scaffolding matrixmaterial particles within a single composite particle). In this case,the composite may exhibit significantly higher robustness duringhandling and battery operation (particularly because of the volumechanges in the volume-changing active material).

As described above, the scaffolding matrix material can be selected as aporous material. The pores is this matrix can be either completelyfilled with the high capacity active material (e.g., when no additionalspace is needed for volume expansion) or partially filled with the highcapacity active material (e.g., when additional pore space is needed toaccommodate the volume expansion during charge-discharge cycling).

The pores in the scaffolding matrix may either be closed or open(interconnected). When direct contact between the electrolyte and activematerial is not desired (for example, when it leads to degradation ofthe active material), the following configurations may be advantageous:(i) most of the pores in the scaffolding matrix material are closed;(ii) several or more interconnected/open pores in the scaffolding matrixmaterial are closed together (in some configurations, all theinterconnected pores within a single particle may be enclosed in anelectrolyte-impermeable but active ion permeable shell); or (iii) thepores may be plugged with another material, which may be used to isolate(at least a majority of) the active material (infiltrated into thescaffolding matrix material) from direct contact with the electrolyte.

The scaffolding material may be sufficiently permeable to electrolyteions participating in the charge storage (such as Li ions in the case ofa Li-ion battery). In this case, even when either (i) no open (nointerconnected) pores exist in the scaffolding matrix material, (ii) thepores are interconnected but not accessible to the electrolyte (e.g.,when an additional ion-permeable shell prevents the electrolyte frompenetrating into the scaffold or when the pores are plugged with anothermaterial), or (iii) the diffusion coefficient of the active material forthe active ions participating in the charge storage is low (e.g., lessthan about 10⁻¹¹ cm²/S), it may be important for the ions from theelectrolyte to reach all the matrix-encapsulated, high-capacity activematerial in a time sufficient to maintain reasonable (for a givenapplication) charge and discharge rates. This will determine the minimumsufficient ionic mobility (diffusion coefficient) and ionic conductivityfor the scaffolding matrix of the above-described composites. The valueof the minimum ionic conductivity of the scaffolding matrix depends onthe size of the composite particles, thickness of the scaffolding matrixwalls, ionic resistance of the active material/scaffolding matrixinterface and other parameters of the system. In most practical cases,it is desirable for the scaffolding matrix to be sufficiently conductiveto maintain at least 50% of the maximum discharge capacity of thecomposite at a discharge rate of “1 C” (which corresponds to the currentdensity capable of discharging the electrode material within 1 hour, ifthe electrode material provides its full capacity).

When no undesirable reactions between the solvent and the high capacityactive material exist, either (i) the walls of the porous ionicallyconductive scaffolding material may be still permeable to electrolytesolvent molecules (e.g., to provide higher ionic conductivity to thescaffolding matrix and allow for higher rate performance of the cell) or(ii) the pores of the scaffolding matrix may be open (interconnected) sothat the ions may propagate to the active material through the openpores filled with electrolyte.

FIGS. 1A-1D illustrate example composite particle compositions accordingto certain example embodiments, comprising a scaffolding matrix material102, 103, 104 and high-capacity active material 101 confined within thescaffolding matrix 102, 103, 104. In some designs, the particlecompositions may retain certain unfilled space forming pores 105. FIG.1A illustrates a closed pore scaffolding matrix particle with poressubstantially fully filled with the high-capacity active material 101.In this case, the scaffolding matrix material 102 is permeable foractive ions (such as Li ions in the case of a Li-ion battery). FIG. 1Billustrates a closed pore scaffolding matrix particle with porespartially filled with the high-capacity active material 101 (and thusleaving some unfilled pores 105). In this case, the scaffolding matrixmaterial 102 is still permeable for active ions (such as Li ions in thecase of a Li-ion battery) but additional pore volume is available forexpansion of the active material 101 during electrochemical reactions(battery cycling). FIG. 1C illustrates a closed pore scaffolding matrixparticle filled with the high-capacity active material 101, but wherethe scaffolding matrix material 103 is porous and permeable toelectrolyte solvent molecules. Porous carbon (e.g., produced bycarbonization of a polymer precursor) is an example of such a matrixmaterial. FIG. 1D illustrates an open pore scaffolding matrix particlewith the pores 105 partially filled with the high-capacity activematerial 101. In this case, the pores within the scaffolding matrixmaterial 104 are interconnected.

For Li-ion battery applications, suitable “volume changing,” “highcapacity,” and “high melting point” active materials may include, butare not limited to, the following: (i) conversion-type electrodes, suchas various metal fluorides (such as lithium fluorides (e.g., LiF), ironfluorides (FeF₃ or FeF₂), manganese fluoride MnF₃, cobalt fluoride (CoF₃or CoF₂), cupper fluoride CuF₂, nickel fluoride NiF₂, lead fluoridePbF₂, bismuth fluorides (BiF₃ or BiF₅), tin fluoride (SnF₂ or SnF₄),antimony fluorides (SbF₃ or SbF₅), cadmium fluoride CdF₂, zinc fluorideZnF₂, and other metal fluorides), various metal chalocogenides (such aslithium sulfide Li₂S, lithium selenide Li₂Se, lithium telluride Li₂Te,and others); (ii) various conversion-type metal chlorides (such aslithium chlorides (e.g., LiCl), iron chlorides (FeCl₃ or FeCl₂),manganese chloride MnCl₃, cobalt chloride (CoCl₃ or CoCl₂), copperchloride CuCl₂, nickel chloride NiCl₂, lead chloride PbCl₂, bismuthchlorides (BiCl₃ or BiCl₅), tin chlorides (SnCl₂ or SnCl₄), antimonychlorides (SbCl₃ or SbCl₅), cadmium chlorides CdCl₂, zinc chloridesZnCl₂, and other metal chlorides); (iii) conversion-type metal bromides(such as lithium bromide LiBr), (iv) conversion-type metal iodides (suchas lithium iodide LiI), (iv) various conversion-type mixed metalfluorides, mixed metal chlorides, mixed metal bromides, mixed metaliodides, mixed metal halides (mixture of two or more metal halides, suchas CuF₂ and FeCl₂ or CuF₂ and FeF₃, etc.); (v) various oxihalides; (vi)various other conversion-type electrodes, their combination and mixture(e.g., sulfides, oxides, nitrides, halides, phosphides, hydrides, etc.);(vii) mixtures and combinations of intercalation-type Li-ion batteryactive materials and conversion-type active materials; and (viii)various high capacity (as previously described) intercalation typeactive materials with high melting points (as previously discussed). Itwill be appreciated that these conversion-type active materials may beutilized in both Li-free or partially lithiated or fully lithiatedstate(s). In some cases, the use of partially or fully lithiatedstate(s) of active materials may be particularly important for aselected synthesis process (e.g., if only the lithiated state issufficiently stable for a particular processing/synthesis route). Itwill be appreciated that partially or fully lithiated conversion-typeactive materials may be composites. In some examples such composites maycomprise metals. For example, if metal halides (e.g., CuF₂ or FeF₃ orothers) are fully lithiated they become a mixture (composite) of alithium halide (e.g., LiF in the case of metal fluorides) and metalclusters (or nanoparticles) of the corresponding metal fluoride (e.g.,Cu, Fe, or a Cu—Fe mixture in the case of CuFe, FeF₃, or a CuFe₂—FeF₃mixture).

For Li-ion battery applications, other suitable “volume changing,” “highcapacity,” and “high melting point” active materials include, but arenot limited to, the following: various alloying-type (where Lielectrochemically alloys with an anode during Li insertion) anodematerials (which may be considered a version of the conversion typeelectrode materials), such as (i) silicon Si, germanium Ge, tin Sn,aluminum Al, lead Pb, antimony An, magnesium Mg, and others. It will beappreciated that that these materials may be doped or heavily or“ultra-heavily” doped; in the case of Si, for example, heavily andultra-heavily doped silicon include silicon doped with a high content ofGroup III elements, such as boron (B), aluminum (Al), gallium (Ga),indium (In), or thallium (Tl), or a high content of Group V elements,such as nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), orbismuth (Bi); by “heavily doped” and “ultra-heavily doped,” it will beunderstood that the content of doping atoms is typically in the range of3,000 parts per million (ppm) to 700,000 ppm, or approximately 0.3% to70% of the total composition); (ii) various binary Si (or Sn, Ge, Al,Mg, etc.) alloys (or mixtures) with other metals; (iii) various ternarySi (or Sn, Ge, Al, Mg, etc.) alloys (or mixtures) with metals; and (iv)other metals and metal alloys that form alloys with Li. It will beunderstood that Group IV elements used to form higher capacity anodematerials may include Ge, Sn, Pb, and their mixtures (e.g. variousalloys or mechanical mixtures), or composites, with the general formulaof Si_(a)—Ge_(b)—Sn_(c)—Pb_(d)—C_(e)-D_(f), where a, b, c, d, e, and fmay be zero or non-zero, and where D is a dopant selected from Group IIIor Group V of the periodic table. For binary silicon alloys (ormixtures) with metals, the silicon content may be in the range ofapproximately 20% to 99.7%. Examples of such alloys (or mixtures)include, but are not limited to: Mg—Si, Al—Si, Ca—Si, Sc—Si, Ti—Si,V—Si, Cr—Si, Mn—Si, Fe—Si, Co—Si, Ni—Si, Cu—Si, Zn—Si, Sr—Si, Y—Si,Zr—Si, Nb—Si, Mo—Si, Tc—Si, Ru—Si, Rh—Si, Pd—Si, Ag—Si, Cd—Si, Ba—Si,Hf—Si, Ta—Si, and W—Si. Such binary alloys may be additionally doped (orheavily doped) with Group III and Group V elements. Alternatively, otherGroup IV elements may be used instead of silicon to form similar alloysor mixtures with metals. A combination of various Group IV elements mayalso be used to form such alloys or mixtures with metals. For ternarysilicon alloys (or mixtures) with metals, the silicon content may alsobe in the range of approximately 20% to 99.7%. Such ternary alloys maybe doped (or heavily doped) with Group III and Group V elements. OtherGroup IV elements may also be used instead of silicon to form suchalloys or mixtures with metals. A combination of various Group IVelements may also be used to form such alloys or mixtures with metals.Examples of other metals and metal alloys that form alloys with lithiuminclude, but are not limited to, Mg, Al, Ga, In, Ag, Zn, Cd, etc., aswell as various combinations formed from these metals, their oxides,etc.

It will be appreciated that these alloying-type active materials may beutilized in both Li-free or partially lithiated or fully lithiatedstates.

For other metal-ion (non-Li) battery applications, suitable “volumechanging,” “high capacity,” and “high melting point” active materialsmay include materials similar to those described above, but where othermetal ions are used instead of Li. For example, for a Na-ion battery,LiBr may be replaced with NaBr as a high capacity, volume changing, highmelting point active material.

For other types of batteries, other “volume changing,” “high capacity,”and “high melting point” materials may be used. For example, for analkaline battery, various metals (such as Fe, Zn, Cd, Ni, or others),various metal oxides, various metal hydrides, various metal hydroxidesand oxihydroxides, or other known conversion-type active electrodematerials may be used as a high capacity anode or cathode material.

In some configurations (for example, in the case of various aqueousbatteries), some aspects of the design (such as the type of compositeparticles, type of scaffolding matrix, protection of the active materialfrom electrolyte, enhancements to mechanical stability or electricalconductivity of the powders, the electrode or powder manufacturingprocess, and others) may be used with active materials that do notexperience phase changes or do not possess very high capacity (e.g.,have specific capacities of only 90-220 mAh/g for the cathode or 90-440mAh/g for the anode)

As previously discussed, advantageous properties of a suitablescaffolding matrix material include: high electrical conductivity (suchas above 10'S/m), good mechanical strength and modulus of toughness, andin some cases (as previously discussed) a high diffusion coefficient forion transport (such as above 10⁻⁹ cm²/s). It may be particularlyadvantageous for the electrical conductivity to be above 0.1 mS/cm(=0.01 mS/mm=0.01 S/m). It may be particularly advantageous for theflexural and compressive strength of the scaffolding matrix material tobe above 1 kPa. The specifications for the thermal properties of thescaffolding matrix may generally depend on the composite synthesisprocedure. If either the active material infiltration into thescaffolding matrix or post-treatment or sealing of some of the pores orother necessary or preferred fabrication steps takes place at elevatedtemperatures, for example, then the scaffolding matrix should besufficiently thermally stable to withstand such a treatment.

Several general classes of scaffolding matrix material have been foundto be suitable. These include, but are not limited to, materialscomprising: (i) carbon (including doped carbon); (ii) conductivepolymers (particularly those that remain conductive during celloperation); and (iii) sufficiently conductive ceramic materials (such asmetal oxides, including mixed or complex metal oxides, phosphates,titanates, silicates, etc.). In some cases, metals may also be suitableas a scaffolding matrix. However, they commonly suffer from corrosion,slow ion transport and limited surface area. Therefore, their use may belimited to certain applications.

For composite electrode materials for Li-ion batteries having an averagepotential below around 4.0 V vs. Li/Li+ during cycling, carbon as ascaffolding matrix may be particularly attractive due to carbon's highelectrical conductivity (mainly, sp² bonded carbon, such as in graphene,graphite, nanotubes, activated carbons, carbon fibers, carbon black andother conductive carbon materials), high mobility for Li ions, highstrength, low density, and (if needed in some cases) good thermalstability.

Various shapes of the composite particles (composed of scaffoldingmatrix filled with active material) may be suitable for differentdesigns, including: flake shapes, elliptical or spherical shapes, aswell as others, including random shapes. However, the use of essentiallyelliptical or near spherical (spheroidal) particles may be beneficialbecause such particles allow for rapid ion transport through theinter-particle spacing within the compacted electrode. Furthermore, incases when the composite particles contain solvent-impermeable shells,it may be beneficial to maintain a narrow distribution of particle sizesduring synthesis and thus control the particle diameter-to-shellthickness ratio in a narrow range. In this case the properties of theparticles may be optimized more precisely and higher energy densitiesmay be achieved with similar reliability/cycle life (or better cyclelife in cells may be achieved with a similar level of energy density).It may therefore be advantageous to maintain a (D90−D10)/D50 ratio ofless than 4 (or even more preferably, less than 3). Once synthesized,particles of mixed sizes may be used in the actual electrode to enhanceits packing density and strength (e.g., where larger particles areadditionally contacted by several smaller particles, the electrodestrength may be increased).

It will be appreciated that the different composite particle structuresprovided herein can be formed in a variety of ways. Several examplemethods of fabrication for an active material infused scaffolding matrixare described below. The fabrication techniques allow efficient andcontrolled incorporation of nanoparticles of electrochemically activehigh capacity battery materials with high melting points, for example,or with no melting point (when the materials would simply decompose athigh temperature), into a porous scaffolding matrix, such as a carbonmatrix by way of example.

In one example, active material may be introduced into pre-fabricatedporous scaffolding matrix (e.g., carbon) particles via chemical vapordeposition (CVD) or atomic layer deposition (ALD) or other vapordeposition techniques. Porous carbon particles may be fabricated bychemical synthesis or precipitation-driven fabrication, or a combinationof chemical and precipitation methods of polymeric precursor particles,their pyrolysis (thermal treatment) and activation (partial oxidation tointroduce or increase the volume of interconnected pores). Desired poresizes and their distribution may be achieved, for example, by acombination of porosity in the polymer precursor and a carbon activationprocess. Another way to produce porous carbon scaffolds includessynthesis of a large polymer monolith, its carbonization, and mechanicalgrinding of the carbon monolith into particles of the desired shape. Theactivation process may involve physical oxidation with oxygen-containinggases (such as CO₂, H₂O, air, O₂, etc.), chemical activation (e.g., withKOH, KNO₃, ZnCl₂, Zn(NO₃)₂, Zn₃(PO₄)₂, H₃PO₄, or other suitablechemicals), or a combination of these approaches. The activation may beperformed during or after the thermal treatment. In order to introduceboth micropores and mesopores (which may in some cases be beneficial, asdiscussed above), carbon activation may be performed at differenttemperatures (e.g., at about 800 and about 1000° C.) or using differentactivation agents (e.g., CO₂ and H₂O). In some cases, it may bebeneficial to introduce mesopores into the porous carbon by utilizing amixture of two polymers or block-copolymers (or carbon yielding polymermixture with an organic liquid or porogen) within the polymericprecursor particles. In some cases, the organic liquid can be anon-solvent for the polymer or the polymer can be swollen in thatliquid. The non-solvent/solvent nature of the liquid will define thepore sizes and distribution of the pores. One of the polymers can beeither removed after synthesis of the polymeric particles by selectiveextraction or one of the polymers may inherently exhibit low thermalstability or very low carbon yield during carbonization or afteractivation, or both. In some cases, pores may be introduced into thesurface of dense carbon particles (such as synthetic or artificialgraphite, mesocarbon microbeads, etc.). In one example, metal or otherinorganic nanoparticles may be pre-deposited on the surface of carbon toserve as catalysts for etching or oxidation of pores within the carbon.In another example, extractable, non-carbonizing nanoparticles may beintroduced into the precursor (e.g., polymer) particles subjected tocarbonizations. In some examples, such nanoparticles may comprise metalsalts, metal oxides, or metals. In some applications, such as when metalnanoparticles are used for pore templating at some point of the porouscarbon synthesis process, it may be advantageous to use metals thatexhibit a melting point in the range from around 100 to around 700° C.It may further be advantageous for this metal not to be flammable uponexposure to air. In, Sn, Cd, Te, and Zn are examples of suitable metals.It may further be advantageous for this metal to exhibit lower toxicity(thus, Cd may be less preferred). In some examples, such metalnanoparticles may be formed upon reduction of the corresponding metalsalts (for example, by carbon). In some examples, this reduction processmay introduce micropores (e.g., pores smaller than 2 nm) into the carbonmaterial. In addition to metals, metal salts, and metal oxides, othertemplates may also be used for pore formation. In other examples, acarbon porous scaffold may be made by carbon deposition (CVD forexample) on a highly porous scaffold made from inorganic material (withpossible etching of the material after carbon deposition). Silicaaerogels are one example of such inorganic scaffolds for carbondeposition. In other examples, the porous carbon scaffolding matrix maybe an activated carbon produced from natural materials (wood, straw, nutshells, natural polysaccharides, coal, sucrose, petroleum coke, pitch,peat, and lignite, to name a few). In other examples, the porous carbonscaffolding matrix may be an activated carbon produced by hydrothermalcarbonization and subsequent annealing and activation of organicprecursors. In yet other examples, the porous carbon scaffolding matrixmay be a porous carbon produced from inorganic precursors (such ascarbides). An example of such a porous carbon synthesis involveschlorination of carbides. A variety of other known methods for theformation of porous carbons may also be utilized.

According to another example method, active particles may be introducedinto a pre-fabricated porous carbon matrix via vapor infiltration and/orcapillary condensation. This approach may be particularly attractive formaterials that have high vapor pressures (e.g., greater than about 0.1Pa) at moderately high temperatures (e.g., less than about 1000° C.).

According to another example method, active particles may be introducedby: (i) dissolving active particles or active particle precursors in asolvent; (ii) infiltration of the solution into the pores of apre-fabricated porous carbon matrix under normal pressure, at increasedpressure, or under vacuum; (iii) evaporation of the solvent; and (iv)(if needed) transformation of the precursor into the active particles(for example, upon heating or upon reaction with a reactive gas orliquid). In some cases, some of the above steps may be repeated toincrease the total amount of the introduced nanoparticles of activematerial into the porous carbon matrix.

According to another example method, active particles may be introducedby: (i) dissolving active particles or active particle precursors in asolvent; (ii) infiltration of the solution into the pores of apre-fabricated porous carbon matrix under normal pressure, at increasedpressure, or under vacuum; (iii) heterogeneous precipitation ofnanoparticles on the inner carbon surface from the solution by, forexample, adding a non-solvent, changing the ionic strength or the pH ofthe solution, or changing the temperature/pressure of the system; and(iv) (if needed) transformation of the precursor into the activeparticles. In some cases, some of the above steps may be repeated orcombined to increase the total amount of the introduced nanoparticles ofactive material into the porous carbon matrix.

According to another example method, active particles may be introducedby infiltration of nanoparticles of active materials into the pores ofpre-formed porous carbon using a suspension infiltration method undernormal pressure, at increased pressures, or under vacuum.

According to another example method: (i) active nanoparticles may firstbe adsorbed onto the surface of the nanoparticles of a polymericprecursor for carbon formation (e.g., by introduction of the oppositecharge on the surface of the active nanoparticles and the surface of thepolymer precursor nanoparticles); (ii) thermal treatment that inducescarbonization of the polymer precursor and the formation of thenanocomposite comprising active nanoparticles, carbon, and nanopores;and (iii) (optional) activation to increase the volume of pores. Inanother example, after the nanoparticle deposition, the compositepolymer particles may be covered with another carbon-forming ornon-carbon forming polymer layer by the electrostatic adsorption of apolymer having opposite surface charge than that of the particles.

According to another example method: (i) active nanoparticles andpolymer precursor nanoparticles may be coagulated heterogeneously from asolution/suspension to form larger composite-precursor particles; (ii)thermal annealing (or “carbonization” in cases when a carbon matrix isto be produced) to form the nanocomposite with nanoparticles uniformlydistributed within carbon and pores; and (iii) optional activation toincrease the volume of pores.

According to another example method, the following may be performed: (i)active nanoparticles may first be dispersed in a monomer or polymersolution; (ii) the produced suspension may be emulsified (e.g., inwater) to produce spherical nanoparticle-polymer colloids in water;(iii) the monomer in the colloids may be polymerized (or solvent may beextracted from a polymer solution) to produce the spherical compositeparticles composed of active nanoparticles and a polymer; (iv) uponwater evaporation the composite particles may be carbonized; and (v) theproduced carbon-active nanoparticle composite may (optionally) beactivated to increase the volume of pores. In another example,polymerization may be conducted in a non-aqueous solvent for a monomer,which is a non-solvent for the polymer being synthesized. During thepolymerization, the polymer particles may be formed by a precipitationmechanism. In the course of the precipitation, polymerization of theactive nanoparticles becomes captured inside the polymer particles. Uponparticle separation, the composite particles may be carbonized.

According to another example method, the following may be performed: (i)water with active particle precursors may be emulsified in a monomersolution; (ii) the produced mixture may be emulsified in water again toproduce colloids of the monomer solution (inside of which there arecolloids of active particle precursor); (iii) the monomer may bepolymerized producing near-spherical polymer particles containing thedistribution of precursors of active particles; (iv) the producedemulsion may be dried, calcinated/carbonized to produce porous carbonparticles with incorporated nanoparticles of active material; and (v)the produced carbon-active nanoparticle composite may (optionally) beactivated to increase the volume of pores. An analogous approach can berealized in a non-aqueous medium as mentioned above.

According to another example method, the following may be performed: (i)an active particle precursor may be dissolved in an organic solventalong with a suitable carbon forming polymer; (ii) the homogeneoussolution may be mixed with an excess of a non-solvent for the particleprecursor and the polymer, and composite particles may be formed byprecipitation; and (iii) the produced particles may be dried,calcinated/carbonized to produce porous carbon particles withincorporated nanoparticles of active material. In another example, theprecipitation may be conducted via changing ionic strength or pH of thesolution, or changing temperature/pressure of the system.

According to another example method, scaffolding matrix material-activematerial composite particles may be produced by: (i) dissolving activeparticles or active particle precursors in a solvent; (ii) dissolvingscaffolding matrix material or scaffolding matrix material precursor inthe same solvent as that used to dissolve active material; (iii) mixingthe two solutions together; (iv) evaporation of the solvent and thusforming precipitates of the active material (or active materialprecursor) within a scaffolding matrix (or within a matrix of thescaffolding material precursor); and (v) (if needed) transformation ofthe active material precursor into the active particles and/ortransformation of the scaffolding material precursor into thescaffolding material (e.g., by thermal treatment in an inert gas orvacuum). In this example, the scaffolding matrix-active materialprecursor solution can be (a) converted into particles (often particlesagglomerated into large granules) by evaporation of the joint solvent,with subsequent (optional) mechanical milling yielding compositeparticles of the desired size; or (b) spray-dried to form particles withthe desired size followed by (if needed) transformation of the activematerial precursor into the active particles and/or transformation ofthe scaffolding material precursor into the scaffolding material (e.g.,by thermal treatment in an inert gas or vacuum).

In addition to the use of the above methods for the preparation ofcarbon-based scaffolding matrix material or carbon-based scaffoldingmatrix material-active material composites, other (non-carbon ornon-pure carbon) scaffolding matrix materials or scaffolding matrixmaterial-active material composites may be prepared by similartechniques or straightforward deviations from such techniques.

Returning to the particle composition discussion above, in some designs,the composition of the scaffolding matrix material may change from thecenter to the perimeter of the composite particle. In one example, thescaffolding matrix may comprise carbon (C), oxygen (O), and hydrogen (H)atoms. In one example, it may be advantageous for the composite particleto exhibit a gradient in the relative content of C, O and H atoms. Inone example, the core of the matrix may contain more O and H (and thus,for example, exhibit higher affinity to some of the active material,while retaining sufficient flexibility to accommodate the volume changeswithin the active material during cycling), while the outer region nearthe perimeter of the particle mostly comprises C atoms to achieve higherelectrical conductivity and a higher elastic modulus. In another exampleof a similar scaffolding matrix, the outermost layer of the scaffold(near the perimeter of the particle) may have a composition that bindswell with the binder material or (in cases when decomposition of theelectrolyte takes place with the formation of solid decompositionproducts—for example, in the case of Li-ion battery electrodes) bindingwell with the SEI, thus improving the stability of the compositeelectrodes during cycling. The outer most layer of the matrix may alsohave a composition that has a relatively poor adhesion (or highinterfacial energy, poor wetting, or longer nucleation time) to the highcapacity active material so that less volume-changing active material islocated near the perimeter of the particle after its synthesis and thusmore stable such particles may be produced. As discussed above, in somedesigns, it may be advantageous for the composite particles to beisolated from the electrolyte by an ionically conductive shell (so that,for example, unfavorable interactions between the active material andthe electrolyte are minimized or avoided). By forming a gradient in thescaffolding matrix composition, the deposition of such a shell layer maybe facilitated, even in cases when the pores in the scaffolding matrixare not completely filled with active material and some pores remainempty to accommodate the volume changes in the active material duringcycling. In one example, the outer most layer of the matrix may haverelatively strong interactions with/adhesion (low interfacial energy) tothe active ion permeable shell material (or, when a vapor depositiontechnique is used for the active material infiltration, exhibit a highsticking coefficient for the active material or active materialprecursor and small nucleation time), thus allowing the shell materialto seal the outer pores within a short distance (for example, withinless than 10% of the particle diameter) and prevent the above-discussedundesirable direct contact of the active material with the electrolytesolvent.

FIGS. 2A-2E illustrate different aspects of example composite particlecompositions according to certain example embodiments, comprising ascaffolding matrix material 202 with a gradient composition and activehigh capacity material 201 confined within the scaffolding matrix 202.FIGS. 2A-2B illustrate such particles without (FIG. 2A) and with (FIG.2B) an active ion permeable shell 203. FIGS. 2C-2E illustrate examplecompositional profiles according to certain example embodiments, wherein FIGS. 2C and 2D the composition changes from the center (core) of theparticle (region “A”) towards the perimeter of the particles (region“B”) and where in FIG. 2E the top surface layer (region “C”) has a stilldifferent composition (e.g., in order to assist in the formation of theparticle shown in FIG. 2B or in order to improve electrode or particleproperties when used in a battery cell).

For some designs, the mechanical properties of the scaffolding matrixmaterial may change from the center of a composite particle to theperimeter of the composite particle. For example, near the center of theparticle the scaffolding matrix material may exhibit lower elasticmodulus or lower hardness so that the volume expansion of the highcapacity material during cycling is easier to accommodate in the centerof the particle. At the same time, for example, near the perimeter ofthe particle the scaffolding matrix material may exhibit higher elasticmodulus and higher strength so that the composite particles may have anability to exhibit small volume changes (which may help retain shape andsize) in spite of the significant volume changes within the activematerial during cycling (which may, for example, be accommodated by thepores and deformable portion of the matrix material).

FIGS. 3A-3D illustrate example profiles of selected mechanicalproperties of the scaffolding matrix material (of the composite particlecompositions) according to certain example embodiments. FIGS. 3A and 3Bshow example profiles of the average hardness (“H”) changes of thescaffolding matrix material along the radius of the composite particlefrom the core (“Hc”) to the surface (“Hs”). FIGS. 3C and 3D show exampleprofiles of the average elastic modulus (“E”) of the scaffolding matrixmaterial along the radius of the composite particle from the core (“Ec”)to the surface (“Es”) to the top surface (“Ets”).

For some designs, the concentration of defects or the degree of disorderwithin the scaffolding matrix material may change from the center to theperimeter of the particles. For example, near the center of the particlethe scaffolding matrix material may exhibit a higher concentration ofdefects or certain functional groups, which, in turn, may serve asnucleation sites for further infiltration with the active material(deposition of the active material within the scaffold material pores).Thus, a higher concentration of nucleation-inducing defects may resultin higher content of the volume changing active material near the centerof the particle, which, in turn, may result in lower overall volumechanges of the composite particle and better electrode stability (cyclelife) for a given active material weight fraction. Near the perimeter ofthe particle, the scaffolding matrix material may exhibit a lowerconcentration of nucleation-inducing defects. If the ion-permeable shellmaterial (discussed above) is similar to the material used in thescaffolding matrix (for example, when both are made of mostly carbonatoms), then a lower concentration of nucleation-inducing defects in thematrix near the perimeter of the particle may assist in the rapiddeposition of such a shell layer (for example, to seal the outer poreswithin a short distance, e.g., within less than 10% of the particlediameter) and prevent the above-discussed undesirable direct contact ofthe active material with the electrolyte solvent. This is because incases of a homo-epitaxial deposition (as opposed to hetero-epitaxialdeposition), the reduced concentration of defects on the substrateresults in a faster growth and a higher quality (fewer vacancies, holes,etc.) of the deposited layer. Thus, even in cases when the pores in thescaffolding matrix are not completely filled with active material (e.g.,when some pores remain empty to accommodate volume changes in the activematerial during cycling), sealing the pores within the thin surfacelayer of the scaffolding matrix-active material composite particle maylargely prevent undesirable solvent-active material interaction, whileretaining intact a large volume of pores (to accommodate volume changesof the active material).

In some designs, the concentration of certain functional groups withinthe scaffolding matrix material may change from the center to theperimeter of the particles. For functional groups that serve asnucleation sites for active material deposition, a higher concentrationin the center of the scaffolding matrix material particles may beadvantageous for achieving a higher content of the volume changingactive material near the center of the final composite particles. Forfunctional groups that, in contrast, prevent the nucleation of theactive material in the pores of the scaffolding matrix material, ahigher concentration in the perimeter of the scaffolding matrix materialmay similarly result in a higher concentration of active material in thecenter of the scaffolding matrix material particles because thenucleation in the perimeter may be delayed.

In some configurations, certain functional groups within the scaffoldingmatrix material may disappear or become undetectable after thedeposition of the active material or other treatments on the compositeparticles (for example, heat treatment or a deposition of anothermaterial, such as a sealing shell material). Therefore, the gradient inthe concentration of certain functional groups may be primarilyimportant during synthesis and may constitute an innovative synthesismethod step to introduce a gradient in the concentration of the activematerial within scaffolding matrix-active material composite particlesor other suitable gradients into the composite particles.

FIGS. 4A-4D illustrate example profiles of the average concentration ofdefects or functional groups of the scaffolding matrix material alongthe radius of composite particles according to certain exampleembodiments. FIGS. 4A and 4B show example profiles of the defectconcentration (“N”) changes of the scaffolding matrix material along theradius of the composite particle from the core (“Nc”) to the surface(“Ns”). FIGS. 4C and 4D show example profiles of the average functionalgroup concentration (“N”) of the scaffolding matrix material along theradius of the composite particle from the core (“Nc”) to the surface(“Ns”).

For some designs, the average spacing between scaffold pores or size ofpores (which may be completely or partially filled with the “volumechanging,” “high capacity,” and “high melting point” active material) ofthe scaffolding matrix material changes from the center of a compositeparticle to the perimeter of the composite particle. In one example,near the core of the composite particle the scaffolding matrix materialmay exhibit lager pores available for filling with active material. Thismay lead to a larger size of the active particles and, in some case, toa larger portion of the high capacity active material near the center ofthe particles. This particle architecture has been found to improveparticle and electrode stability during cycling. In cases when it may bedesirable to seal the remaining scaffold pores (and most of the activematerial dispersed within the pores) with a protective ion-permeableshell material layer (as previously described), smaller pores near theperimeter of the particles may assist in doing so within a short (e.g.,less than 10% of the particle diameter) distance. As previouslydiscussed, sealing the pores within the thin surface layer of the(scaffolding matrix-active material) composite particle largely preventsundesirable solvent-active material interaction, while retaining intacta large volume of the pores (to accommodate volume changes of the activematerial).

In another example, the outer-most layer of the active material mayexhibit the largest pores. These large pores may remain mostly emptywith respect to the active material (or, if needed, with respect to thesealing shell material) and potentially serve multiple purposes: (i)prevent sintering (gluing) particles together during/after shelldeposition (if such shell(s) are deposited); (ii) increase the particleroughness and improve the strength of the particle-binder bonding, theparticle-particle bonding, or the particle-SEI bonding (all of whichtypically improve the cycle stability and other performancecharacteristics of electrodes made of such composites); (iii)electrically connect the composite particles within the electrode (ifthe scaffolding matrix material is electrically conductive); and (iv)serve to uniformly separate particles from each other in an electrode(this may be particularly useful for stress minimization within anelectrode when particles expand during the first and subsequent cycles,and may be even more particularly important when the electrode capacityloading is in excess of approximately 2 mAh/cm² and when the electrodeactive material expands by more than approximately 8 vol. %); to name afew.

For some designs, the average pore volume of the scaffolding matrix(which may be completely or partially filled with the “volume changing,”“high capacity,” and “high melting point” active material) may changefrom the center of a composite particle to the perimeter of thecomposite particle.

FIGS. 5A-5C illustrate example composite particle and scaffolding matrixcompositions according to certain example embodiments, where thescaffolding matrix material 502 changes in average pore size along theparticle radius from the center (core) to the perimeter. FIG. 5Aillustrates a composite particle with, for example, a scaffolding matrix502 having closed pores filled with high capacity active material 501,where the scaffold pore size reduces from the center to the perimeter ofthe particle. FIG. 5B illustrates, in relevant part, only thescaffolding matrix 502 (of the composite particle) having, for example,open interconnected pores 503, where the pore size reduces from thecenter to the perimeter of the particles. FIG. 5C illustrates, inrelevant part, only the scaffolding matrix 502 (of the compositeparticle) having, for example, open interconnected pores 503, where thepore size initially reduces from the center to an area closer to thesurface of the particle and then increases again at the surface(perimeter) of the particle, thus forming a “buried layer” having thesmallest pore size.

In some designs, the fraction of the “surface layer” or the fraction ofthe “buried layer” may range from around 1 to around 50 vol. % of thetotal volume of the particle.

The thickness of the layer of the scaffolding matrix with small pores(such as the “surface layer” or “buried layer”) may vary depending onthe chemistry and application of the composite particles. However, athickness in the range from 2 nm to 500 nm has been found to work wellin many applications.

FIGS. 6A-6C illustrate example profiles of the average pore size withinexample scaffolding matrix compositions along the radius of theparticles, according to certain example embodiments. FIGS. 6A and 6Billustrate example profiles of the average pore size of a scaffoldingmatrix with smaller pore sizes closer to the perimeter of the particle.The suitable pore size (“D”) distribution may depend on the particularchemistry of active material and the ion mobility within a composite,but typically the suitable average pore size in the center of theparticles (“Dc”) may range from 2 to 800 nm, while the suitable averagepore size in the surface layer (“Ds”) may range from 0.3 to 100 nm. Insome embodiments, it may be advantageous for Dc to be at least twice aslarge as Ds. FIG. 6C illustrates an example profile of the average poresize of the scaffolding matrix, where the very top surface layer of thescaffolding matrix has larger pores compared to the “buried small porelayer” (which may be sealed with a shell material in cases when thepores of the scaffolding matrix are interconnected and when the activematerial does not completely fill the pores). The average pore size atthe top surface layer of the particles (“Dts”) may range, for example,from around 1.5 to 50 nm, which has been found to work well in manyapplications.

FIGS. 7A-7C illustrate example profiles of the average pore volumewithin example scaffolding matrix compositions along the radius of theparticles, according to certain example embodiments. FIGS. 7A and Billustrate example profiles of the average pore volume of thescaffolding matrix with smaller pore volumes closer to the perimeter ofthe particle. The suitable pore volume (“V”) distribution may depend onthe particular chemistry of the active material (and the related volumeexpansion) and the ion mobility within a composite, but typically thesuitable average pore volume of the scaffold in the center of theparticles (“Vc”) may range from around 0.2 to around 10 cc/g, which hasbeen found to work well, while the suitable average pore volume in thesurface layer (“Vs”) may range from 0.01 to 5 cc/g, which has also beenfound to work well in some applications. A pore volume in the center ofthe particles smaller than 0.2 cc/g may lead to an undesirable reductionin the volumetric capacity of the composite because it may not permit asufficient amount of the volume changing active material to be placedinto these pores. In some embodiments, it may be advantageous for Vc tobe at least twice as larger as Vs. FIG. 7C illustrates an exampleprofile of the average pore volume of the scaffolding matrix, where thevery top surface layer of the scaffolding matrix has more pores (largerpore volume) compared to the “buried layer with smaller pore volume”(which may be sealed with a shell material in cases when the pores ofthe scaffolding matrix are interconnected and when the active materialdoes not completely fill the pores). The average pore volume at the topsurface layer of the particles (“Vts”) may range from around 0.4 toaround 20 cc/g, which has been found to work well in many applications.

For some designs, more than one property of the scaffolding matrix (forexample, more than one of the previously discussed properties) maychange from the center of a composite particle to the perimeter of thecomposite particle. In one example embodiment, the scaffolding matrixmay exhibit, for example, changes in pore size from the center to theperimeter of the particle and additionally exhibit changes incomposition from the center to the perimeter of the particle. Thisfacilitates favorable combinations of properties whenscaffold-comprising composite particles are produced and used inbatteries.

For some designs, the orientation of scaffolding material pores within acomposite particle may change from the center of the particle towardsthe perimeter of the particle. For example, in the center of theparticle, the pores may be oriented either randomly or have somepreferred orientation along the radial direction, while near theperimeter (surface) of the particles, the pores (e.g., slit-shapedpores) may be preferentially oriented parallel to the particle surface(and thus perpendicular to the radial direction). Such a variation inthe pore orientation may bring multiple benefits. In cases when it maybe desirable to seal the internal pores within a thin shell layer, itmay be necessary to slow down the transport of shell precursor moleculesfrom the outside of the particles towards the center of the particles.By orienting slit-shaped pores parallel to the surface, the diffusionpath for the shell precursor molecules may be efficiently increased. Inother words, such a pore orientation near the particle surface increasesthe tortuosity of the path towards the center of the particle. In caseswhen such a shell layer is deposited, from a vapor phase, for example,increasing the actual path to the level where it exceeds an averagedistance of the precursor molecule travel prior to its decomposition(and deposition of the shell material) by, for example, an order ofmagnitude, allows the internal particle pores to be sealed within asmall fraction (e.g., approximately 10%) of the diameter. The layer ofthe slit-shaped (and, for example, smaller) pores within which thesealing “shell” layer is deposited may be termed a “sealable porouslayer.” In another example, it may be desirable to have a layer ofrandomly oriented or radially oriented (and, for example, larger) poresat the surface of the particles outside the “sealable porous layer”discussed above. This porous layer may remain mostly empty from both theactive material and from the sealing shell material after theirdeposition and potentially serve multiple purposes (as previouslydiscussed), including: (i) prevent sintering (gluing) particles togetherduring/after the shell deposition within a “sealable porous layer;” (ii)increase the particle roughness and improve the strength of theparticle-binder bonding, the particle-particle bonding, or theparticle-SEI bonding; and (iii) electrically connect the compositeparticles within the electrode (if the porous outer layer iselectrically conductive).

FIGS. 8A-8B illustrate example scaffolding matrix compositions accordingto certain example embodiments, where the scaffolding matrix material802 changes in pore orientation along the particle radius from thecenter (core) to the perimeter. FIG. 8A illustrates a scaffolding matrix802 (for the composite particle), where the center (core) of thescaffolding matrix particle exhibits mostly randomly oriented (orspherical) pores, which gradually change orientation to become orientedalong the radial direction, which, in turn, change orientation to becomeoriented perpendicular to the radial direction at the top surface of thescaffolding particles. FIG. 8B illustrates a scaffolding matrix 802 (forthe composite particle), where the center (core) of the scaffoldingmatrix particle exhibits pores oriented either along the radialdirection or randomly oriented, and where the pores change orientationto become oriented perpendicular to the radial direction near thesurface of the scaffolding particle, and where the pores become randomlyoriented (or oriented along the radial direction) at the top surface ofthe particle.

The thickness of the layer of the scaffolding matrix with porespreferentially oriented perpendicular to the radial direction may varydepending on the chemistry and application of the composite particles.However, a thickness in the range from 2 nm to 200 nm has been found towork well in many applications.

In some designs, it may be advantageous for the scaffolding matrixmaterial to be a composite comprising two or more materials. Suchmaterials may provide different (e.g., complementary) functionalitiesand exhibit differences in electronic, ionic, thermal, chemical,mechanical, or other properties. For example, one of the compositecomponents may exhibit better mechanical strength, while another mayexhibit better electrical conductivity or better protection of theactive material against undesirable side reactions, or provide morefavorable heterogeneous nucleation sites to the active material duringcomposite synthesis or provide another useful function or combination offunctions. In some designs, it may be advantageous for at least onecomponent of such a composite scaffolding matrix material to exhibit agradual change in at least one property (density, electricalconductivity, ionic conductivity, thermal stability, chemicalcomposition, elastic modulus, hardness, or another property) from thecenter to the perimeter of the scaffolding matrix material.

Various methods may be utilized to produce scaffolding particles withvariable composition. According to some suitable methods for compositeparticle formation, scaffolding matrix particles with gradually changingcomposition may be produced first and subsequently infiltrated withactive material and optionally a protective layer (which may be solid orliquid) and/or a protective shell. According to other suitable methodsfor composite particle formation, a scaffolding matrix of variablecomposition may be produced simultaneously with the formation of thecomposite particles.

A suitable method of scaffolding matrix-comprising composite particlesynthesis, where the scaffolding matrix exhibits variable compositionalong the radius of the particles, may comprise, for example: (i)forming a suspension of nanoparticles of active materials coated withone composition of a precursor of matrix material (such as one type ofscaffolding matrix precursor, referred to for generality below as a“type A” scaffolding precursor); (ii) forming another suspension ofnanoparticles of active material coated with another composition of aprecursor of matrix material (such as another type of scaffolding matrixprecursor, referred to for generality below as a “type B” scaffoldingprecursor); (iii) inducing a gradual aggregation of the type A precursorcoated nanoparticles of active material from the nanoparticlesuspension; (iv) over time adding suspension of the type B precursorcoated nanoparticles of active material from the nanoparticle suspensionsuch that more and more of the type B precursor coated nanoparticles areattached to the outer layer of the aggregate particles; (v) optionallycoating the outer layer of the aggregate particles with another (shelllayer) of nanoparticles or a layer of the type A, type B, or another(“type C”) precursor matrix material; (vi) stabilizing the formedaggregate particles (with the composition of the precursor for thescaffolding matrix gradually changing from the center to the outerperimeter) in a suspension and separating them from the solvent: and(vii) transforming the precursor material of the matrix to the suitablescaffolding matrix material (for example, by a thermal treatment) andthus obtaining aggregate particles with gradually changing (from thecenter of the particles to the perimeter of the particles) compositionof the scaffolding, wherein the scaffolding matrix material of each ofthe composite aggregate particles structurally supports the activematerial, electrically interconnects the active material, and assists inminimizing changes in volume of the aggregate particles in spite ofchanges in volume of the active material.

Another example of a suitable method of scaffolding matrix-comprisingcomposite particle synthesis, where the scaffolding matrix exhibitsvariable composition along the radius of the particles, may comprise,for example: (i) forming a solution (or suspension of nano-clusters) ofone type of a precursor of matrix material (referred to for generalitybelow as a “type A” scaffolding precursor); (ii) forming a solution (orsuspension of nano-clusters) of another type of a precursor of matrixmaterial (referred to for generality below as a “type B” scaffoldingprecursor); (iii) inducing a gradual aggregation of the type A precursorthus causing the growth of the scaffolding matrix precursor particles;(iv) over time adding a solution (or suspension of nanoclusters) of thetype B precursor such that more and more of the type B precursor areattached to the outer layer of the aggregate particles changing itscomposition gradually; (v) optionally coating the outer layer of theaggregate A-B composite precursor particles with another (shell layer)of another (“type C”) precursor matrix material; (vi) stabilizing theformed scaffolding matrix precursor aggregate particles (with thecomposition of the precursor for the scaffolding matrix graduallychanging from the center to the outer perimeter) in a suspension andseparating them from the solvent; (vii) transforming the precursormaterial of the matrix to the suitable scaffolding matrix material (forexample, by an oxidation and a thermal treatment, which may include aporosity enhancement by activation) and thus obtaining scaffoldingmatrix particles with gradually changing (from the center of theparticles to the perimeter of the particles) composition of thescaffolding; and (viii) filling the scaffolding matrix material withactive material, optionally coating the surface of the active materialwith a protective layer and optionally forming a protective shell toprevent or minimize reaction of the active material with ambient air(during storage or slurry preparation) or with electrolyte (duringbattery operation).

Yet another example of a suitable method of scaffoldingmatrix-comprising composite particle synthesis, where the scaffoldingmatrix exhibits variable composition along the radius of the particles,may comprise, for example: (i) nucleating particles consisting of onetype of a precursor of a matrix material (referred to for generalitybelow as a “type A” scaffolding precursor) by a vapor deposition (suchas a CVD or ALD) process (in, e.g., a tubular furnace); (ii) introducinga gradually increasing amount of another type of a precursor of matrixmaterial (referred to for generality below as a “type B” scaffoldingprecursor) along the reactor, causing simultaneous particle growth and agradual change in particle composition; (iii) optionally coating theouter layer of the aggregate A-B composite precursor particles withanother (shell layer) of another (“type C”) precursor matrix material;(iv) transforming the precursor material of the matrix to the suitablescaffolding matrix material (for example, by an oxidation and anadditional thermal treatment, which may include a porosity enhancementby activation) and thus obtaining scaffolding matrix particles withgradually changing (from the center of the particles to the perimeter ofthe particles) composition of the scaffolding; (v) filling thescaffolding matrix material with active material, optionally coating thesurface of the active material with a protective layer and optionallyforming a protective shell to prevent or minimize reaction of the activematerial with ambient air (during storage or slurry preparation) or withelectrolyte (during battery operation). It will be appreciated thatfilling of the scaffolding matrix material with an active material mayalso be performed simultaneously with scaffold particle formation byfeeding active material precursor into the reactor where scaffoldparticles are formed.

For the formation of composite particles with tunable (along the radius)scaffolding matrix toughness, elastic modulus, hardness, or othermechanical properties, similar methods can be used as for thefabrication of composite particles with tunable scaffolding matrixcomposition. In this case though, it may be beneficial for themechanical properties of interest to vary significantly with varying ofthe precursor composition.

For the formation of composite particles with a tunable (along theradius) scaffolding matrix microstructure, similar methods can be usedas for the fabrication of composite particles with tunable scaffoldingmatrix composition. In this case though, it may be beneficial for themicrostructure of the scaffolding material to vary significantly withvarying of the precursor composition (even if the scaffolding matrixmaterial composition is similar—for example,CH_(y)O_(z)N_(w)S_(u)P_(v)Cl_(t)F_(s), where the y, z, w, u, v, t, and snumbers are in the range of approximately 0 to approximately 5 and wherethese numbers are normalized by the atomic fraction of C in thiscomposition).

Various methods may be utilized to produce scaffolding particles withvariable pore shape and pore orientation along the radius of theparticles. The methods may vary depending on the desired degree ofcontrol and the composition of the scaffolding matrix material. Forexample, in cases where the scaffolding matrix comprises mostly carbon,the scaffolding matrix particles can be prepared by thermal treatment(annealing in controlled environment with optional oxidation andactivation, depending on a particular chemistry) of the organicprecursor particles. The pore shape and orientation in the scaffoldingmatrix particles often depends on the properties and structuralorientation of the precursor particles. Thus, by first preparing theprecursor particles, where the precursor composition and orientationchanges from the core to the surface, scaffolding particles can beproduced with variable pore shape and pore orientation along the radiusof the particles. Furthermore, the porous carbon scaffold precursor canalso be produced by activation of non-porous carbon, produced forexample, by CVD. The CVD-deposited carbon (particularly if deposited atlow pressures below 50 Torr or at high temperatures above 500° C.)typically exhibits some degree of grain orientation (ordering). Wheninducing the pores in such a CVD-deposited carbon by activation, poresmay be produced with a preferred direction parallel to the originalorientation of grains within the CVD carbon. Thus, by (i) first CVDdepositing a layer on the surface of carbonized polymer particles andthereby producing a CVD carbon coating with grains oriented mostlyparallel to the particle surface and then (ii) activating the CVD-Ccoated particles (e.g., by physical and chemical activation) carbonscaffolding matrix particles can be produced with pores largely orientedperpendicular to the radial direction (parallel to the surface) withinthis surface layer of the scaffolding particles. In the bulk of thescaffolding matrix particles, at the same time, the pores may beoriented, for example, randomly.

Various methods may be utilized to produce scaffolding particles withvariable pore size (or pore volume) along the radius of the particles.The methods may vary depending on the desired degree of control and thecomposition of the scaffolding matrix material. For example, in caseswhere the scaffolding matrix comprises mostly carbon, the scaffoldingmatrix particles can be prepared by thermal treatment of organicprecursor particles, as previously described. The pore size and porevolume in the scaffolding matrix particles typically depends on theproperties and structural orientation of the precursor particles (forgiven thermal treatment conditions). For example, some of the precursormaterial may induce formation of large pores, some may induce formationof smaller pores, some may nearly completely disappear during theparticular thermal treatment, some may induce larger pore volume andsome smaller. Thus, by first preparing the scaffold precursor particles,where precursor composition changes from the core to the surface (aspreviously described), scaffolding particles can be produced withvariable pore size and pore volume along the radius of the particles. Inanother suitable example method, the carbonization yield of the carbonprecursor (for example, when suitable polymers are used as carbonprecursors) may depend on the oxidation conducted prior to thecarbonization (annealing) procedure. By introducing a gradient in thedegree of oxidation from the center to the perimeter of the carbonprecursor particles (for example, by controlling the time andtemperature of the exposure of the precursor particles to a suitableliquid or gaseous oxidizing agent, which may be used to control itsdiffusion distance from the perimeter/surface of the precursor particlesto the center of the precursor particles), one may achieve the desiredlevel of the gradient in the carbon porosity after the carbonization.Additional pore volume may be formed by an additional activation step.

When additional porosity into the carbon particles is introduced byactivation of previously formed carbon particles, different rates ofactivation processes may be used to create a desired pore sizedistribution. Activation rates can be tuned by varying the chemicalnature of the carbon precursors constituting the particles.

For some designs, the composition of the high capacity active materialmay change from the center to the perimeter of the composite particle.This change in composition provides various advantages when thecomposite material is used in batteries.

For example, in Li-ion battery materials, various high capacitymaterials are differentiated in various parameters (which may beimportant for Li battery operation and cost), such as capacity, cost,volume changes during Li insertion and extraction, average potential forLi insertion and extraction, and reactivity (or solubility) in contactwith liquid electrolyte, to name a few. It may be advantageous for thecomposite particle to have, for example, more of a higher capacitymaterial (that exhibits the largest volume changes) infiltrated into thecenter of the particle, and have more of another, lower capacitymaterial (that exhibits smaller volume changes) infiltrated into thesurface layer of the composite particle. In this case, the overallstability of the particle may be improved. In an illustrative examplewhen metal fluorides are used as a high capacity Li-ion cathode materialwithin a scaffolding matrix, a composite core may be rich, for example,in a higher volume changing (and higher capacity) FeF₃, while thesurface may be rich, for example, in a lower volume changing (and lowercapacity) FeF₂. In another example, it may be advantageous to have moreof a higher capacity (or higher energy density) (but potentially morereactive with electrolyte) material in the core and have more of a lessreactive with electrolyte (or less dissolvable in electrolyte) materialnear the surface of the composite particle (even if such a materialoffers lower capacity or lower energy density to the cell). In thiscase, again, the overall electrode and/or cell stability may besignificantly improved. In cases when metal fluorides are used as a highcapacity Li-ion cathode material within a scaffolding matrix, acomposite core may be rich, for example, in a highly soluble (and higherenergy density) CuF₂ (or in a Cu—LiF composite if a fully lithiatedstate of the cupper fluoride is used in the particle synthesis ordesign), while the surface may be rich, for example, in a significantlyless soluble (and lower capacity) FeF₂ or Fe—F—O (iron oxy fluoride) (oran Fe—LiF or FeO₂—LiF—Li₂O composite if a fully lithiated state of theiron fluoride is used in the particle designs). In yet another example,it may be advantageous (in some applications) to have more of a materialthat is active at a lower level of discharge in the core of the particleand have more of a material that is active at a higher level ofdischarge closer to the surface of the composite particle. In this case,during discharge, the volume of the active material in the core of theparticles changes first, while the volume of the active material nearthe particle surface changes significantly only at a higher level ofdischarge. Since the number of shallow discharge cycles is typicallymore than deep discharge cycles, the frequency of significant volumechanges in the active material near the surface of the compositeparticles will be smaller and the resulting cell stability higher. Incases when metal fluorides are used as a high capacity Li-ion cathodematerial within a scaffolding matrix, a composite core may be rich, forexample, in CuF₂ (which has a higher average potential during itselectrochemical reaction with Li) (or in a Cu—LiF composite if a fullylithiated state of the cupper fluoride is used in the particle synthesisor design) while the surface may be rich, for example, in a BiF₃ orBi—O—F (bismuth oxi-fluoride) (which have lower average potential) ortheir partially or fully lithiated analogs. In some examples, mixing ofdifferent active materials (such as metal fluorides or LiF-metalmixtures in the case of fluoride-based active materials for use inrechargeable metal-ion, such as Li-ion, or rechargeable metal, such asLi, batteries) within the composite may be at an atomic level (as insolid solutions or mixture of solid solutions and clustering). In caseswhen high capacity fluoride-comprising active materials are used, insome examples a gradient in the relative fraction of LiF-to the metal(e.g., Cu or Fe) from the center to the perimeter of the compositeparticles may be advantageous for applications in batteries. In caseswhen high capacity Li-ion anode materials are confined within ascaffolding matrix, a composite core may be rich, for example, in Si(which has a relatively low average potential of Li extraction fromlithiated silicon) while the surface may be rich, for example, in Si—O(partially oxidized silicon), Sn, Sn—O (partially oxidized tin), Si—Sn—O(partially oxidized silicon-tin alloy), Si—Mg, P (phosphorous), As(arsenic), Bi (bismuth), or other high capacity materials that haverelatively higher average Li extraction potential.

FIGS. 9A-9D illustrate example compositions of active material confinedwithin a scaffolding matrix according to certain example embodiments,where the active material changes composition along the particle radiusfrom the center (core) to the perimeter. In the illustration, adifference in shading symbolizes different active material compositions.FIGS. 9A and 9C illustrate example embodiments where the scaffoldingmatrix 902 is uniform, while FIGS. 9B and 9D illustrate exampleembodiments where the scaffolding matrix 903 is also changing from thecenter to the perimeter of the particles. FIGS. 9A and 9B illustrateexample embodiments where the active material 901 fills the scaffoldpores completely, while FIGS. 9C and 9D illustrate example embodimentswhere the active material 901 fills the scaffold pores only partially,leaving some pore 904 volume for active material expansion duringbattery operation.

FIGS. 10A-10C illustrate examples of the profiles for the changes inaverage composition of active material along the particle radius fromthe center (core) to the perimeter according to certain exampleembodiments, where the active material is confined within a scaffoldingmatrix. As shown, the composition may change in different ways from thecore (region “A”) to the surface (region “B”) to even a top surface(region “C”) portion of the particle.

For some designs, the hardness of the high capacity active material maychange from the center to the perimeter of the composite particle. Thischange in hardness (particularly the change in hardness in the expandedstate of the active material) provides various advantages when thecomposite material is used in batteries. Overall, it may be advantageousfor the high capacity active material to exhibit low hardness (be soft)(particularly in the expanded state) so that it can plastically deformduring expansion and better adapt to the shape of the scaffolding matrixmaterial pore. In most applications, however, where such a high capacityactive material exhibits significant volume changes, it may be moreimportant for the active material to be soft near the surface of thecomposite particles than in the core. Indeed, harder active materialnear the surface will result in higher (for a given pore volume andfraction of the active material) volume changes near the surface, which,in turn, may induce formation of cracks and separation of the particleswithin an electrode (e.g., due to the breakage of contact with abinder).

For some designs, the elastic modulus of the high capacity activematerial may change from the center to the perimeter of the compositeparticle. A lower value of elastic modulus of the active materialresults in a smaller resistance of the composite to elastic deformation,which may be important for both calendaring (densification) of theelectrode and minimizing composite volume changes during active materialexpansion. Therefore, a lower value of elastic modulus may be beneficialfor both maximizing electrode volumetric capacity (and thus maximizingcell energy density) and maximizing electrode stability during cycling(and thus maximizing cycle life of the cell). However, materials with alower elastic modulus do not necessarily exhibit the highest energydensity when used in cells. Accordingly, reducing the average value ofthe elastic modulus near the surface of the particles may be moreimportant than doing so in the core. Thus, for some batteryapplications, it may be advantageous to utilize composite particles withlower elastic modulus active material(s) near the particle surface.

FIGS. 11A-11D illustrate examples of the profiles for the changes in theselected mechanical properties of active material (such as hardness inFIGS. 11A and 11B, and modulus in FIGS. 11C and 11D) along the particleradius from the center (core) to the perimeter according to certainexample embodiments, where the active material is confined within ascaffolding matrix. FIGS. 11A and 11B show example profiles of theaverage hardness (“H”) of the active material along the radius of thecomposite particle from the core (“Hc”) to the surface (“Hs”). FIGS. 11Cand 11D show example profiles of the average elastic modulus (“E”) ofthe active material along the radius of the composite particle from thecore (“Ec”) to the surface (“Es”) to the top surface (“Ets”).

For some designs, the density of the high capacity active material maychange from the center of a composite particle to the perimeter of thecomposite particle. Higher density of the active material in the core ofthe composite particles may result in a higher density of the core ofthe composite particles. Such particles may yield more uniformelectrodes, which, in turn, typically result in better cell performancecharacteristics. Lower density of the active material near the perimeterof the particles may also be linked to the presence of pores within suchactive material. The presence of pores, in turn, reduces the hardness,elastic modulus, and overall volume changes in the active material,which (as discussed above) may be more important to minimize near thesurface of the composite particles than in the center.

For some designs, the density of the composite particle may change fromthe center to the perimeter of the composite particle. In one example,the highest density may be disposed near the center of the compositeparticle. When processed into electrodes, such particles may offer morestable performance in cells.

FIGS. 12A-12B illustrate examples of the profiles for the changes indensity of active material along the particle radius from the center(core) to the perimeter according to certain example embodiments, wherethe active material is confined within a scaffolding matrix. As shown,the density (“d”) may change in different ways from the core (“dc”) tothe surface (“ds”).

For some designs, the weight fraction of the high capacity activematerial (to the total weight of the composite) may change from thecenter of a composite particle to the perimeter of the compositeparticle. A lower fraction of the high capacity active material andhigher fraction of the scaffolding matrix material near the perimeter ofthe composite particles typically enhances stability of the particlesduring cycling (for example, due to minimizing volume changes within thesurface layer of the composite particles). In some applications, ahigher fraction of the high capacity active material near the core ofthe particles increases the energy density of the electrodes based onsuch particles, while typically only moderately reducing its cyclestability.

FIGS. 13A-13B illustrate examples of the profiles for the changes in therelative weight fraction (Wa/Wsm) of active material (“Wa”) relative tothe scaffolding matrix (“Wsm”) (or the scaffolding matrix and the restof the composite, including the protective coating and the protectiveshell or additional filler material, if present in the composite) alongthe particle radius from the center (core) to the perimeter according tocertain example embodiments, where the active material is confinedwithin a scaffolding matrix. The suitable relative weight fraction inthe core of the particle (Wa/Wsm)_(c) or near the surface (Wa/Wsm)_(s)may vary depending on the application and particular chemistry. However,for many applications the (Wa/Wsm)_(c) may preferably be the range from0.5 to 30, and (Wa/Wsm)_(s) may preferably be in the range from 0 to 5.

For some designs, the volume fraction of the high capacity activematerial (to the total volume of the composite) may change from thecenter of a composite particle to the perimeter of the compositeparticle. A lower volume fraction of the high capacity active materialnear the perimeter of the composite particles reduces cycling-inducedstresses near the surface of the particles, which enhances the electrodestability during cycling and thus cell cycle life. For example, in caseswhere high capacity anode materials for Li-ion batteries (e.g.,Si-comprising materials) are used, increasing both the pore volume andthe volume occupied by the scaffolding matrix material greatly enhancescycle stability of the cells comprising such composite electrodesparticles. Such a relative volume increase of the scaffold and pores maybe more important near the surface of the active particles. Compared touniform composite particles of identical theoretical energy density,composite particles with a higher volume fraction of the active materialin the center generally exhibit better performance characteristics, suchas better cycle stability.

FIGS. 14A-14B illustrate examples of the profiles for the changes in therelative volume fraction (Va/Vo) of active material (“Va”) relative tothe total or overall volume (“Vo”) of the composite along the particleradius from the center (core) to the perimeter according to certainexample embodiments, where the active material is confined within ascaffolding matrix. The suitable relative volume fraction in the core ofthe particle (Va/Vo)_(c) or near the surface (Va/Vo)_(s) may varydepending on the application and particular chemistry, and whether ornot the active material is already in the expanded state. However, formany applications the (Va/Vo)_(c) may preferably be within the rangefrom 0.1 to 60 and (Va/Vo)_(s) may preferably be in the range from 0 to6. The suitable average value of the relative volume fraction of theactive material within a composite should be larger than 0.1 but smallerthan 60. An average volume fraction of the active material that is lessthan 0.1 may significantly limit the volumetric capacity of thecomposite-based electrodes and the resulting energy density of thebattery cells utilizing such composites. An average volume fraction ofthe active material that is greater than 60 typically limits thecomposite particle stability or rate performance to an unsatisfactorylevel.

Various methods may be utilized to produce active material-scaffoldingcomposite particles with a variable composition of the active materialalong the particle radius. In some methods of composite particleformation, the scaffolding matrix particles may be produced first andsubsequently gradually infiltrated with active material of variablecomposition, as well as with an optional protective layer and protectiveshell. In other methods of composite particle formation, the variablecomposition of active material may be produced simultaneously with theformation of the composite particles.

An example method of scaffolding matrix and active material comprisingcomposite particle synthesis, where the active material exhibits avariable composition along the radius of the particles, may comprise,for example: (i) forming a suspension of nanoparticles of activematerial “A” (or active material A precursor) coated with the precursorof scaffolding matrix material (such as one type of scaffolding matrixprecursor); (ii) forming another suspension of nanoparticles of activematerial “B” (or active material B precursor) coated with the precursorof matrix material; (iii) inducing a gradual aggregation of the type Aactive material (or its precursor) nanoparticles from the nanoparticlesuspension; (iv) over time adding suspension of the type B activematerial (or its precursor) nanoparticles such that more and more of thetype B coated nanoparticles are attached to the outer layer of theaggregate particles; (v) optionally coating the outer layer of theaggregate particles with another (shell layer) of a precursor matrixmaterial; (vi) stabilizing the formed aggregate particles in asuspension and separating them from the solvent: and (vii) transformingthe precursor material of the matrix (and, if relevant, the precursoractive material) to the suitable composite of scaffolding matrix filledwith active material (for example, by a thermal treatment) and thusobtaining aggregate particles with gradually changing (from the centerof the particles to the perimeter of the particles) composition of theactive material, wherein the scaffolding matrix material of each of thecomposite aggregate particles structurally supports the active material,electrically interconnects the active material, and assists inminimizing the changes in volume of the aggregate particles in spite ofchanges in volume of the active material.

Another example method of scaffolding matrix-comprising compositeparticle synthesis, where the active material exhibits variablecomposition along the radius of the particles, may comprise, forexample: (i) forming scaffolding matrix material particles; (ii) forminga solution of one type (type “A”) active material precursor that wetsthe scaffolding matrix material; (iii) forming a solution of anothertype (type “B”) active material precursor; (iv) infiltrating solution Ainto the core of the matrix particles and drying this solution (by theaction of capillary condensation the active material precursor A willmostly precipitate into the core of porous matrix particles); (v)transforming the precursor into active material A (for example, bythermal treatment); (vi) repeating steps (iv) and (v) several times,gradually replacing at least some of the precursor solution A with theprecursor solution B, thus producing scaffolding matrix particles filledwith gradually changing (from the center of the particles to theperimeter of the particles) composition of the active material; (vii)optionally coating the surface of the active material with a protectivelayer; and (viii) optionally forming a protective shell to prevent orminimize reaction of the active material with the electrolyte (duringbattery operation).

Another example method of scaffolding matrix-comprising compositeparticle synthesis, where the active material exhibits variablecomposition along the radius of the particles, may comprise, forexample: (i) either nucleating particles consisting of one type ofprecursor matrix material by a CVD process in a tubular furnace orintroducing a pre-formed scaffolding matrix material powder into thefurnace; (ii) feeding active material precursor (referred to forgenerality below as a “type A” active material precursor) into thereactor where scaffold particles are formed in order to infiltrate thescaffold with the active material A (or its precursor A); (iii) feedinganother active material precursor (referred to for generality below as a“type B” active material precursor) into the reactor at a later stage,where scaffold particles pre-infiltrated with the precursor A (or activematerial A) (e.g., mostly in the core of the particles) could be theninfiltrated with the active material B (or a precursor B) thus forming adesired gradient of active materials (A-B) within each compositeparticle; (iv) optionally coating the outer layer of the A-B-scaffoldmaterial composite particles with a shell layer of another (e.g., “typeC”) precursor matrix material; and (v) if needed, transforming theprecursor material of the matrix to the suitable scaffolding matrixmaterial, thus obtaining scaffolding matrix particles with graduallychanging (from the center of the particles to the perimeter of theparticles) composition of the active material.

For the formation of composite particles with tunable (along the radius)active material hardness, elastic modulus, or other mechanicalproperties, similar methods may be employed as for the fabrication ofcomposite particles with a tunable active material composition. In thiscase, though, it may be advantageous that the mechanical properties ofinterest vary significantly with varying of the composition of theselected active materials.

Various methods may be utilized to produce composite scaffoldingmatrix-active material particles with variable size of active materialparticles along the radius of the particles. The methods may varydepending on the desired degree of control and the composition of boththe scaffolding matrix material and active material.

In one example, the scaffolding matrix particles may be prepared firstand have gradually changing surface chemistry or pore size properties.In this case, filling the scaffolding matrix particles with activematerial (either through gaseous phase deposition or through solutionchemistry infiltration and optional subsequent thermal treatment) mayinduce the desired gradient in the size of the active materialparticles.

Another example method of scaffolding matrix and active materialcomprising composite particle synthesis, where the active materialexhibits variable particle size along the radius of the particles, maycomprise, for example: (i) forming a suspension of size “1” (e.g.,large) nanoparticles of active material coated with precursorscaffolding matrix material; (ii) forming a suspension of size “2”(e.g., smaller) nanoparticles of active material (or its precursor)coated with precursor scaffolding matrix material; (iii) forming asuspension of size “3” (e.g., still smaller) nanoparticles of activematerial (or its precursor) coated with precursor scaffolding matrixmaterial; (iv) inducing a gradual aggregation of the size 1 activematerial (or its precursor) nanoparticles from the nanoparticlesuspension; (v) over time adding suspension of the size 2 activematerial (or its precursor) nanoparticles so that more and more of thesize 2 coated nanoparticles are attached to the outer layer of theaggregate particles; (vi) over time adding suspension of the size 3active material (or its precursor) nanoparticles so that more and moreof the size 3 coated nanoparticles are attached to the outer layer ofthe aggregate particles; (vii) optionally coating the outer layer of theaggregate particles with another (shell layer) of a precursor matrixmaterial; (viii) stabilizing the formed aggregate particles in asuspension and separating them from the solvent; and (ix) transformingthe precursor material of the matrix (and, if relevant, the precursoractive material) to the suitable composite of scaffolding matrix filledwith active material (for example, by a thermal treatment), thusobtaining aggregate particles with gradually changing (from the centerof the particles to the perimeter of the particles) size of the activematerial, wherein the scaffolding matrix material of each of thecomposite aggregate particles structurally supports the active material,electrically interconnects the active material, and assists inminimizing the changes in volume of the aggregate particles in spite ofthe changes in volume of the active material.

When scaffold particles with gradual pore sizes are formed first, activematerial in a suspension form can be infiltrated into the particles.Utilization of active material suspensions with particle sizes 1, 2, and3 (as discussed above) provide the ability to achieve a desired activeparticle size distribution within a scaffold particle.

Various methods may be utilized to produce composite scaffoldingmatrix-active material particles with a weight fraction of activematerial varying along the radius of the particles. The methods may varydepending on the desired degree of control and the composition of boththe scaffolding matrix material and active material.

In one example, the scaffolding matrix particles may be prepared firstand have a gradually changing pore size or gradually changing porevolume. In this case, filling the scaffolding matrix particles withactive material (either through gaseous phase deposition or throughsolution chemistry infiltration and optional subsequent thermaltreatment) may induce the desired gradient in the weight fraction of theactive material along the radial direction of the particles.

Another example method of scaffolding matrix and active materialcomprising composite particle synthesis, where the active materialexhibits a variable weight fraction along the radius of the particles,may comprise, for example: (i) forming a suspension of size “1”nanoparticles of active material coated with a layer of a giventhickness of precursor scaffolding matrix material; (ii) forming asuspension of size “2” nanoparticles of active material (or itsprecursor) coated with precursor scaffolding matrix material of the samethickness as size 1; (iii) inducing a gradual aggregation of the size 1active material (or its precursor) nanoparticles from the nanoparticlesuspension; (iv) over time adding suspension of the size 2 activematerial (or its precursor) nanoparticles of active material from thenanoparticle suspension so that more and more of the size 2 coatednanoparticles are attached to the outer layer of the aggregate particles(since the thickness of the scaffold material precursor coating may bethe same for both sizes of the particles, gradual addition of the size 2active material nanoparticles results in a gradual change in the weightfraction of the active material); (v) optionally coating the outer layerof the aggregate particles with another (shell layer) of a precursormatrix material; (vi) stabilizing the formed aggregate particles in asuspension and separating them from the solvent; and (vii) transformingthe precursor material of the matrix (and, if relevant, the precursoractive material) to the suitable composite of scaffolding matrix filledwith active material (for example, by a thermal treatment), thusobtaining aggregate particles with gradually changing (from the centerof the particles to the perimeter of the particles) weight fraction ofthe active material, wherein the scaffolding matrix material of each ofthe composite aggregate particles structurally supports the activematerial, electrically interconnects the active material, and assists inminimizing changes in volume of the aggregate particles in spite ofchanges in volume of the active material.

Another example method of scaffolding matrix and active materialcomprising composite particle synthesis, where the active materialexhibits a variable weight fraction along the radius of the particles,may comprise for example: (i) forming a suspension of nanoparticles ofactive material coated with a layer of thickness “T1” of precursorscaffolding matrix material; (ii) forming a suspension of nanoparticlesof active material (or its precursor) coated with precursor scaffoldingmatrix material of a different thickness “T2;” (iii) inducing a gradualaggregation of the active material (or its precursor) nanoparticles fromthe first nanoparticle suspension; (iv) over time adding the secondsuspension of active material (or its precursor) nanoparticles so thatmore and more of the nanoparticles coated with a different thicknesslayer are attached to the outer layer of the aggregate particles (sincethe thickness of the scaffold material precursor coating may bedifferent for both suspensions, gradual addition of the second type ofactive material nanoparticles results in a gradual change in the weightfraction of the active material); (v) optionally coating the outer layerof the aggregate particles with another (shell layer) of a precursormatrix material; (vi) stabilizing the formed aggregate particles in asuspension and separating them from the solvent: and (vii) transformingthe precursor material of the matrix (and, if relevant, the precursoractive material) to the suitable composite of scaffolding matrix filledwith active material (for example, by a thermal treatment), thusobtaining aggregate particles with gradually changing (from the centerof the particles to the perimeter of the particles) weight fraction ofthe active material, wherein the scaffolding matrix material of each ofthe composite aggregate particles structurally supports the activematerial, electrically interconnects the active material, and assists inminimizing changes in volume of the aggregate particles in spite ofchanges in volume of the active material.

Another example method of scaffolding matrix-comprising compositeparticle synthesis, where the active material exhibit variable weightfraction along the radius of the particles, may comprise, for example:(i) either using pre-formed scaffold material “A” particles ornucleating scaffold particles consisting of one type of precursor matrixmaterial (referred to for generality below as a “type A” scaffoldingprecursor) by a CVD process in a tubular furnace; (ii) adding anincreased amount of another type of precursor matrix material (referredto for generality below as a “type B” scaffolding precursor) along thereactor, causing gradual change in particle composition; (iii) feedingactive material precursor into the reactor where scaffold particles areformed to achieve desired weight fraction distribution of activematerial in the particle; (iv) optionally coating the outer layer of theaggregate A-B composite particles filled with active material withanother (shell layer) of another (e.g., “type C”) precursor matrixmaterial; and (v) transforming the precursor material of the matrix tothe suitable scaffolding matrix material, thus obtaining scaffoldingmatrix particles with a gradually changing (from the center of theparticles to the perimeter of the particles) weight fraction of activematerial.

Various methods could be utilized to produce composite scaffoldingmatrix-active material particles with a volume fraction of activematerial varying along the radius of the particles. The methods may varydepending on the desired degree of control and the composition of boththe scaffolding matrix material and active material.

In one example, the scaffolding matrix particles may be prepared firstand have a gradually changing pore size or gradually changing porevolume. In this case, controlled filling of the scaffolding matrixparticles with active material (either through gaseous phase depositionor through solution chemistry infiltration and optional subsequentthermal treatment) may induce the desired gradient in the volumefraction of the active material along the radial direction of theparticles.

Another example method of scaffolding matrix and active materialcomprising composite particle synthesis, where the active materialexhibits a variable volume fraction along the radius of the particles,may comprise, for example: (i) identifying two precursors for activematerial that yield different volume fractions of the active materialafter transformation or heat treatment (referred to for generality belowas precursors “A” and “B”); (ii) forming a suspension of nanoparticlesof type A precursor coated with a layer of precursor scaffolding matrixmaterial; (iii) forming a suspension of nanoparticles of type Bprecursor coated with a layer of precursor scaffolding matrix material;(iv) inducing a gradual aggregation of the type A active materialprecursor nanoparticles from the nanoparticle suspension; (v) over timeadding suspension of the coated type B active material precursornanoparticles from the nanoparticle suspension so that more and more ofthe type B coated nanoparticles are attached to the outer layer of theaggregate particles; (vi) optionally coating the outer layer of theaggregate particles with another (shell layer) of a precursor matrixmaterial; (vii) stabilizing the formed aggregate particles in asuspension and separating them from the solvent; and (viii) transformingthe precursor active materials A and B to the suitable composite ofscaffolding matrix filled with active material (for example, by athermal treatment). Because different precursors yield different volumefractions of the active material, aggregate particles obtained in thisway exhibit gradually changing (from the center of the particles to theperimeter of the particles) volume fraction of the active material,wherein the scaffolding matrix material of each of the compositeaggregate particles structurally supports the active material,electrically interconnects the active material, and assists inminimizing changes in volume of the aggregate particles in spite ofchanges in volume of the active material.

Another example method of scaffolding matrix and active materialcomprising composite particle synthesis, where the active materialexhibits a variable volume fraction along the radius of the particles,may comprise, for example: (i) identifying a pore former (e.g., materialthat produces pores upon decomposition or completely decomposes upon aparticular stimulus, such as heat treatment, or can completely dissolvein a solvent that does not dissolve or unfavorably affect that scaffoldmaterial precursor and active material) that is miscible with aprecursor of the scaffolding matrix material; (ii) forming a suspensionof active material nanoparticles (or active material precursornanoparticles) coated with a layer of the precursor scaffolding matrixmaterial; (iii) forming a suspension of active material nanoparticles(or active material precursor nanoparticles) coated with the layer ofprecursor scaffolding matrix material mixed with the pore formermaterial; (iv) inducing a gradual aggregation of the active material (orprecursor) nanoparticles from the suspension of active materialnanoparticles (or active material precursor nanoparticles) coated withthe layer of the precursor of scaffolding matrix material mixed with thepore former material; (v) over time adding suspension of the coatedactive material (or precursor) nanoparticles from the regularnanoparticle suspension so that less and less pore forming material isincorporated into the outer layer of the aggregate particles; (vi)optionally coating the outer layer of the aggregate particles withanother (shell layer) of a precursor matrix material; (vi) stabilizingthe formed aggregate particles in a suspension and separating them fromthe solvent; and (vii) transforming the precursor material to thesuitable composite of scaffolding matrix filled with active material(for example, by a thermal treatment). Because the pore former increasespore volume, aggregate particles obtained in this way exhibit graduallychanging (from the center of the particles to the perimeter of theparticles) volume fraction of the active material, wherein thescaffolding matrix material of each of the composite aggregate particlesstructurally supports the active material, electrically interconnectsthe active material, and assists in minimizing changes in volume of theaggregate particles in spite of changes in volume of the activematerial.

Similarly, a CVD process utilizing scaffold precursors “A” and “B,” withsimultaneous feeding of active material into the CVD precursor, may beanother suitable method of scaffolding matrix and active materialcomprising composite particle synthesis, where the active materialexhibits a variable volume fraction along the radius of the particles.

For some designs, more than one property of the active material (forexample, more than one of the previously discussed properties) may beconfigured to change from the center to the perimeter of the compositeparticle. As an example, the active material may exhibit changes inparticle size or particle shape from the center to the perimeter of theparticle and additionally exhibit changes in the composition from thecenter to the perimeter of the particle. This allows various favorablecombinations of properties when active material-scaffolding matrixcomposite particles are produced and used in batteries.

For some designs, both the high capacity active material and thescaffolding matrix may change from the center to the perimeter of thecomposite particle. In this case, at least one of the properties of thescaffolding matrix (composition, structure, porosity, pore shape, poresize, pore orientation, pore volume, elastic modulus, density, hardness,etc.) may change from the center of a composite particle to theperimeter of the composite particle and at least one of the propertiesof the active material (composition, structure, porosity, size, elasticmodulus, density, hardness, etc.) may change from the center of thecomposite particle to the perimeter of the composite particle. Thisallows various favorable combinations of properties when such compositeparticles are used in batteries. FIGS. 9B and 9D illustrate two examplesof such simultaneous changing properties of the scaffolding matrix andactive material within a single composite particle.

For some designs, the high capacity active material confined (e.g.,infiltrated) within a scaffolding matrix material may be coated with athin and in some cases conformal layer of a so-called “protective”material. The purpose of such a protective layer may range fromprotection of the active material against its reaction with ambient air(such as oxidation) to the protection of the active material againstunfavorable reactions with the electrolyte. A thickness of theprotective layer from approximately 0.2 nm to approximately 10 nm hasbeen found to work well. The composition of the protective layer dependson a particular chemistry of the active material and the cell. Forexample, in the case of Si, Sn, Sb, Al, Fe, and other metal-based activematerials using a protective layer comprising C and, in some cases, Hatoms (e.g., with C atoms comprising at least 20% of the atomic fractionof the protective layer composition), has been found to work well.

As discussed above, for certain active materials of interest (e.g.,silicon anodes or metal halide cathodes in the case of Li-ionbatteries), the storing and releasing of these ions (e.g., Li ions in aLi-ion battery) causes a substantial change in volume of the activematerial, which, in conventional designs, may lead to irreversiblemechanical damage, and ultimately a loss of contact between individualelectrode particles or between the electrode and underlying currentcollector. Moreover, it may lead to continuous growth of the SEI aroundsuch volume-changing particles, particularly on the anodes. The SEIgrowth, in turn, consumes Li ions and reduces cell capacity. Formationof scaffold-active material composites overcomes some of thesechallenges or significantly reduces their impact. In some designs asprovided for herein, electrode stability may be further enhanced by a“shell” coating, where such a coating is permeable for active ions(e.g., a metal ion in the case of a metal-ion battery, such as a Li ionin the case of a Li-ion battery) but not permeable to electrolytesolvent. Such a shell protects active material from unfavorableinteractions with the electrolyte. An average thickness of such a shelllayer from about 1 nm to about 200 nm (preferably from 3 nm to 60 nm)has been found to work well.

For some designs, this shell layer may be located near or at the surfaceof the composite particles. In some configurations, such a shell layermay fill the remaining void (pore) space within the portion of thescaffolding matrix material near the perimeter of the compositeparticles. In this case, undesired sintering (or gluing) of neighboringcomposite particles by the shell layer may be avoided during shellformation when the shell layer is deposited within, not outside of, thecomposite particles.

For some designs, the scaffolding matrix material may substantiallypenetrate through the shell material. For example, this design may beused for the scaffolding matrix to strengthen the shell. As anotherexample, when the scaffolding matrix exhibits high electrolyte ionconductivity, this penetration of the scaffolding matrix enhances therate performance of the particles and the corresponding cells assembledwith electrodes produced with such particles. As another example, whenthe scaffolding matrix exhibits high electrical conductivity while thesealing shell layer material exhibits lower electrical conductivity,this penetration of the scaffolding matrix through the shell layerenhances both the capacity utilization and the rate performance of theparticles. In some configurations (for example, when the surface or bulkionic conductivity of the scaffolding matrix material is sufficientlyhigh) the shell material (interpenetrating with the scaffolding matrixin the perimeter of the composite particles) may not be ionicallyconductive. In some configurations the shell material may be solid. Insome configurations (for example, when the shell material exhibits lowmiscibility with an electrolyte) the shell material may be liquid.

The protective shell may be advantageously deposited in a particularregion of the scaffolding matrix. For some designs, a protective “shell”coating may infiltrate a porous scaffolding matrix (partially pre-filledwith active material particles) in a surface or near-surface region ofthe composite particles that is characterized by having smallerscaffolding material pores compared to the pores in the core of theparticles. For some designs, a protective shell coating may infiltrate aporous scaffolding matrix (partially pre-filled with active materialparticles) in a surface or near-surface region of the compositeparticles that is characterized by having scaffolding material porespreferentially oriented parallel to the particle surface. For somedesigns, a protective shell coating may infiltrate a porous scaffoldingmatrix (partially pre-filled with active material particles) in asurface or near-surface region of the composite particles that ischaracterized by having scaffolding material with a lower concentrationof defects compared to that of the core of the particles.

For some designs, the shell material may be at least partially depositedfrom a vapor phase via vapor deposition methods. Examples of suchmethods include, but are not limited to, chemical vapor deposition (CVD)(including chemical vapor infiltration), atomic layer deposition (ALD),plasma-enhanced ALD, plasma-enhanced CVD, vapor infiltration, andothers.

For some designs, the shell material may be at least partially depositedfrom a solution. Examples of such suitable methods include sol-gel,layer-by-layer deposition, polymer adsorption, surface initiatedpolymerization, layer formed by nanoparticles adsorption, and others.

For some designs, the shell material may comprise a polymer. In someconfigurations, it may be advantageous for such a polymer to be anionically conductive polymer. Multiple routes may be utilized in orderto deposit such a polymeric material on the surface of a scaffoldingmatrix material (including matrix material infiltrated with a highcapacity active material). For example, polymerization initiators may beattached to the surface of the porous particles where the target polymerwill be grafted, thus forming a thin film (or a coating) of the polymer.As another example, polymers may be first prepared in solution and thenattached onto the surface of the particles by using a “graft onto”method. The thickness of the polymer film may be tuned by changing themolecular weight of the polymer. In another example method, a polymermay be deposited using a CVD deposition route.

For some designs, the shell may be a “smart” composite, which can reactto, for example, temperature increasing above some threshold value(e.g., above around 60-100° C.) and upon reaching such a temperatureeffectively prevent either electrical connectivity of the compositeparticles with other particles and the current collector or ionicconnectivity of the composite particles with the electrolyte (forexample, by reducing such conductivities by a significant degree—e.g.,from around 2 times to around 2,000,000,000,000 times). Such a propertymay be particularly useful for batteries with flammable organicelectrolytes that may experience thermal runaway, such as Li-ionbatteries with low potential anodes (e.g., Si, C, Li, Sn, Sb, Al, andothers). In this case, the smart shell may act as a particle-levelsafety mechanism, shutting down electrochemical reactions within thebattery cell upon the cell overheating.

Various mechanisms may be utilized for the formulation of such a smartcomposite shell that reduces electrical conductivity at elevatedtemperatures. For example, such a shell may comprise a dense brush-likecoating composed of an electrically conductive and thermally responsivepolymer “A” and electrically insulative and thermally stable material“B” (e.g., ceramic particles or nanowires or another polymer), whereeach polymer chain of A is tethered to the particle surface from one endand is expanding beyond the material B in a regular state. At ambienttemperature, the regions rich with polymer A work as electricallyconductive wires connecting the particles to each other and a currentcollector. However, once the temperature is increased above somerelatively high value (e.g., above 80-120° C.), the length of thepolymer A will decrease (shrink) so that the outer surface of thecoating will become insulative B, thus stopping the electricalconnectivity of the individual particles and thus shutting down (ordramatically decreasing the rate of) the electrochemical reactions.

Various mechanisms may be also utilized for the formulation of such asmart composite shell that reduces ionic conductivity at elevatedtemperatures. For example, such a shell may comprise A-B type blockcopolymers, where A is an ion conductive polymer and B is an ionnonconductive polymer. The volume ratio may be tuned betweenapproximately 10% and 30% for the block A to find the optimum ratio forobtaining a cylindrical morphology (with cylinders positionedperpendicular to the shell). Such an architecture may have cylinders ofblock A placed into a matrix of block B. These cylinders may be in thetens of nanometers dimension and used as channels to transfer ionsbetween the particles. Once the temperature of the medium rises abovethe order-disorder temperature for the block copolymer, the cylindricalconductive channels will become disassembled and mixed with the B block,which will stop or significantly decrease the ionic conductivity of theshell.

FIGS. 15A-15D illustrate example composite particle compositionsaccording to certain example embodiments, comprising a scaffoldingmatrix material 1502 and high capacity active material 1501 confinedwithin the scaffolding matrix 1502, and a protective shell 1503enclosing the composite particles and protecting the active materialfrom unfavorable interactions with electrolyte solvent or ambientenvironment. FIGS. 15A-15C illustrate example composite particleformulations with the shell 1503 being deposited on the surface of thecomposite particles. FIG. 15D illustrates an example composite particleformulation with the shell 1503 being deposited in the sub-surface ofthe composite particles, within the outer portion of the scaffoldingmatrix 1502.

For some designs, the outer layer of the composite electrode particlesmay exhibit a high roughness or a high surface area, or both. Asdiscussed above, the composite particles (comprising high capacity, highvolume changing materials infiltrated into the scaffolding matrix) mayexhibit significantly smaller volume changes during cell operation thanthe high capacity materials by themselves. However, they may also sufferfrom slightly larger volume changes (and sometimes from smaller averageparticle sizes) compared to intercalation-type materials. When aprotective shell is applied to such particles, they often tend to bondtogether, forming large agglomerates. These undesirable factors maycontribute to their undesirably faster degradation, lower power, andreduced volumetric energy storage characteristics. Formation of highroughness on the surface of such particles may overcome theirshortcomings and improve their performance in battery cells. Highroughness, for example, enhances bonding of the particle surface to abinder and, in some cases (when the electrolyte decomposes on theparticle surface forming a surface layer) to an SEI layer. Highroughness may also prevent gluing the particles together, forming powderaggregates during the deposition of the shell layer (or, at least,making such a gluing very weak and easy to break without damaging theparticles). Weakly bonded aggregates may be broken with a mild millingpost-processing. In some cases, high roughness may allow electrons totunnel easier from one particle to the next when the separation distanceis relatively small (less than around 5-10 nm). This is because highroughness may induce electric-field concentrated areas near the tips ofthe hills, which bends the vacuum energy level and increases tunnelingprobability. Peak-to-valley roughness from 0.5 nm to 500 nm on theparticle surface has been found to work well. A high surface area of thetop layer may similarly enhance particle bonding with the binder or SEIand, in some cases, effectively induce sufficient roughness and fieldconcentration to enhance electron tunneling and thus conductivity (andrate performance) of the electrode. A surface layer with an internalsurface area from 2 to 200 times higher than the geometrical surfacearea of the perimeter of the composite particle has been found to workwell. A porous material coating (e.g., a porous carbon coating) with anaverage pore size ranging from 2 to 50 nm has been found to work well.

For some designs, the outer rough or high surface area layer of thecomposite electrode particles may be electrically conductive. Examplesof suitable rough layer materials include, but are not limited to,metals, carbon, conductive polymers, and conductive ceramics (such asconductive oxides and nitrides). In cases of high capacity compositeanode materials for Li-ion batteries, first cycle losses may beminimized when this layer does not contain electronegative elements inits composition. For some designs, the outer rough or high surface arealayer of the composite electrode particles may have a polar surface. Inthis case, such a surface bonds well with an SEI and most of the bindersused in typical Li-ion battery electrodes. When selecting a surfacecoating for the composite particles, it may be beneficial to ensure thatthe coating material does not unfavorably (chemically orelectrochemically) react with the electrolyte or electrolyte ions duringbattery operation. For example, Al may work well as a coating materialfor Li-ion battery cathodes, but not anodes, because itelectrochemically reacts with Li. Similarly, Cu or Ni (Cu, inparticular) may work well for some of the Li-ion battery anodes, but maycorrode (oxidize) if used in high voltage (above around 3-3.5 V)cathodes.

FIGS. 16A-16D illustrate example composite particle compositionsaccording to certain example embodiments, comprising a scaffoldingmatrix material 1602 and active high capacity material 1601 confinedwithin the scaffolding matrix (and optionally a protective shell), andhaving a rough or high surface area outer surface. FIG. 16A illustratesan example composite particle with a porous (preferably electricallyconductive) surface layer 1603. FIG. 16B illustrates another examplecomposite particle coated with (preferably electrically conductive)nanoparticles 1604. FIG. 16C illustrates yet another example compositeparticle exhibiting a rough surface coating of preferably electricallyconductive material 1605. FIG. 16D illustrates yet another examplecomposite particle coated with nanoflakes, nanowires, or nanotubes ofelectrically conductive material 1606.

For some designs, the protective shell layer on the surface of thecomposite particles (which prevents undesirable interaction between theelectrolyte and active material) may be electrically isolative orionically insulative (not conducting active ions, such as Li ion in thecase of a Li-ion battery), or both. While access to both electrons andions may be necessary during operation of a battery (so thatelectrochemical reactions can proceed), such function(s) may beconducted by the nano-wires, nanotubes, or nano-sheets deposited on thesurface or core of the core-shell particles and penetrating through theshell material layer. In this case, these wires/tubes/sheets/particleseither (i) ionically connect the inner portion of the core-shellcomposite particles with electrolyte, (ii) electrically connect theinner portion of the composite particles with other particles and thecurrent collector, or (iii) conduct both functions (provide electricaland ionic pathways to the inner portion of the core-shell compositeparticles). In cases when the shell material is not conductive foreither electrons or ions, or both, this gives more flexibility in theselection of such materials and thus may reduce the core-shell compositecost and improve its mechanical properties. In addition, in cases whenthe composite is used for a low-voltage anode (e.g., a Si-comprisinganode), reduction in the electrical conductivity in the shell may reducethe total SEI formed and thus reduce the cell first cycle losses.

FIGS. 17A-17C illustrate example composite particle compositionsaccording to certain example embodiments, comprising a scaffoldingmatrix material 1702 and high capacity active material 1701 confinedwithin the scaffolding matrix and a protective shell 1703, and whereconductive elements 1704 (e.g., wires, tubes, sheets, or particles)penetrate through the shell layer 1703, without (FIGS. 17A-17B) or with(FIG. 17C) pores 1705.

For some designs, the protective shell may be a responsive composite,which changes either electrical or ionic conductivity upon heating toabove 100° C., thus providing a particle-level safety mechanism forbatteries (such as flammable Li-ion batteries).

For some designs, at least one property of the active material maychange from the center of a composite particle to the perimeter of thecomposite particle and, at the same time, the composite particle mayexhibit a rough or high surface area surface. Such a combination of bulkand surface properties of the composite particles may enhance theirperformance in cells. As an example, the active material may exhibitchanges in particle size from the center to the perimeter of theparticle and additionally exhibit a rough (preferably conductive) outersurface (as shown in FIGS. 16B, 16C, and 16D).

For some designs, at least one property of the scaffolding matrixmaterial may change from the center to the perimeter of the compositeparticle and, at the same time, the composite particle may exhibit arough or high surface area surface. Such a combination of bulk andsurface properties of the composite particles may similarly enhancetheir performance in cells. As an example, the scaffolding matrixmaterial may exhibit changes in pore size, pore orientation, or poredensity from the center to the perimeter of the particle andadditionally exhibit a rough (preferably conductive) outer surface (asshown in FIGS. 16B and 16D).

For some designs, at least one property of the scaffolding matrixmaterial may change from the center to the perimeter of the compositeparticle, and, at the same time, at least one property of the activematerial may change from the center to the perimeter of the compositeparticle. Such a combination of bulk and surface properties of thecomposite particles may similarly enhance their performance in cells.

Various methods may be utilized for the formation of a rough surface ofthe particles. For example, an outer portion of the porous scaffoldingmay be coated with particles of various shape (including rough dendriticparticles and near spherical particles), fibers, nanowires, ornanoflakes by electrodeposition. As another example, an outer portion ofthe porous scaffolding material may be coated with particles,nanofibers, nanowires, nanoflakes, or rough dendritic particles byvarious vapor deposition techniques, including chemical vapor deposition(CVD), including catalyst-assisted CVD, plasma-assisted CVD, and others.

Various methods may be utilized for the formation of a porous coatinglayer on the surface of composite particles. For example, an outerportion of the porous scaffolding may be exposed to the electrolyte. Asanother example, the porous layer of an electrically conductive materialmay be deposited via electrodeposition. As another example, the porouslayer may be produced by the deposition of a polymer (or a polymermixture) layer and its subsequent annealing (and partial decomposition)and optional activation.

LiBr and LiI have not been conventionally used as active cathodematerials for Li-ion batteries comprising liquid electrolytes because ofthe high solubility of such salts in electrolyte solvents and lowelectrical conductivity. Such materials, however, exhibit high capacityand energy density. In addition, LiBr is relatively inexpensive.Embodiments provided herein may be used to overcome the inherentlimitations of LiBr (and LiI) and allow their use as high capacityactive cathode materials. As previously described, for some designs, thescaffolding matrix-active material composites may comprise either LiBror LiI as a high capacity active material for Li-ion battery cathodes.In this case, the pores in the scaffolding matrix may be either closed(preferred, in order to avoid dissolution of Br₂ and LiBr inelectrolyte) or sealed with an external shell material layer prior tocell assembling, or both (in the last case, the external shell aroundthe LiBr confined in the closed pores of the scaffolding matrix may beadded for enhanced robustness, enhanced conductivity, or enhanceddispersion in a slurry or other functions). Furthermore, it may bepreferable that the LiBr (or LiI)-comprising scaffold materialcomposites do not exhibit empty pores.

In the case of composite materials comprising LiBr (or LiI) within ascaffolding matrix, it may be beneficial for the scaffold material notto involve any undesirable reactions with liquid Br₂ (or I₂) producedupon extraction of Li. Therefore, most metals may not work well asscaffolding materials. Instead, metal oxides, conductive carbon, andselected conductive polymers may work well. However, I and Br permeatethrough most conductive polymers and, in some cases, additionally reducetheir conductivity, which is undesirable. Conductive carbon works wellas both the scaffolding and the shell material. In some applications, itmay be advantageous for the composite particles to have an additionalshell comprising a metal oxide. Such an additional shell layer may alsocomprise traditional intercalation-type cathode material, preferablyexhibiting Li insertion and extraction in a similar voltage range asLiBr (or LiI). Lithium iron phosphate is an example of a suitableintercalation-type cathode material. In this case, the probability of Ior Br diffusion through the carbon layer into the electrolyte (andeventually irreversibly reducing on the anode) may be minimized.

Various methods of fabricating a battery electrode compositioncomprising composite particles with enhanced properties are alsoprovided.

For some designs, a suitable method may comprise, for example: (i)forming porous, electrically-conductive scaffolding matrix particles(for example, porous carbon particles) with (physical, microstructural,mechanical, or chemical) properties changing from the center of theparticles to the perimeter of the particles; (ii) partially filling thescaffolding matrix particles with an active material to store andrelease ions during battery operation, whereby the storing and releasingof the ions causes a substantial change in volume of the activematerial, and wherein the scaffolding matrix structurally supports theactive material, electrically interconnects the active material, andaccommodates the changes in volume of the active material; (iii) coatingthe composite particles with a protective layer material (for example,by using chemical vapor deposition methods); and (iv) mixing theproduced composite particles with a binder solution and conductiveadditives, and casting on a conductive metal current collector.

Another suitable method may also comprise, for example: (i) formingmultiple suspensions of uniform nanoparticles of active materials coatedwith a precursor of matrix material (for example, coated with a polymerlayer as a precursor for a carbon matrix material); (ii) inducing agradual aggregation of the largest coated nanoparticles of activematerial from the nanoparticle suspension; (iii) over time adding asuspension of the smaller and smaller coated nanoparticles so that suchsmaller and smaller particles are attached to the outer layer of theaggregate particles; (iv) optionally coating the outer layer of theaggregate particles with nanoparticles or a layer of the precursormatrix material; (v) stabilizing the formed aggregate particles (withsizes of their nanoparticle building blocks gradually changing from thecenter to the outer perimeter) in a suspension and separating them fromthe solvent: (vi) transforming the precursor material of the matrix tothe electrically-conductive scaffolding matrix material (for example, bya thermal treatment), thus obtaining aggregate particles with graduallychanging (from the center to the perimeter of the particles) properties,wherein the scaffolding matrix material of each of the compositeaggregate particles structurally supports the active material,electrically interconnects the active material, and assists inminimizing changes in volume of the aggregate particles in spite ofchanges in volume of the active material; (vii) optionally depositing anadditional protective layer on the surface (or within the top layer) ofthe particles by a vapor deposition technique (e.g., by chemical vapordeposition); and (viii) mixing the produced composite particles with abinder solution and conductive additives, and casting on a conductivemetal current collector.

One of the useful functions of the scaffolding matrix material particlesmay be to define dimensions of the composite particles. By controllingthe size distribution of the scaffolding matrix particles one can thuscontrol the size distribution of the composite particles. In order toincrease the volumetric capacity of the electrode comprising suchcomposite particles it may be advantageous to utilize particles ofdifferent size in order to increase the packing density of the compositeparticles in the electrode. For example, smaller composite particles maybe placed in the electrode in the interstitial positions of the largerparticles. Smaller particles may also allow electrode to provide fasterresponse to current pulse demands due to smaller diffusion distances.Adding smaller particles to the electrode may also enhance theelectrode's mechanical strength and resilience. It may also beadvantageous for the material in the smaller and larger scaffoldingmatrix particles to exhibit different properties (e.g., be more rigid ormore conductive in the case of the smaller particles). It may be alsoadvantageous for the material in the smaller and larger compositeparticles to exhibit different properties or compositions (e.g., usedifferent active materials or different fractions of active material inthe smaller and larger particles) in order to achieve the most favorableperformance at the cell (or electrode) level. In one example method, anelectrode with more favorable properties may be produced by: (i)producing scaffolding matrix material powders of an average size “1”(for generality); (ii) producing scaffolding matrix material powders ofan average size “2”; (iii) producing composite particles A from thescaffolding matrix material powders of an average size 1; (iv) producingcomposite particles B from the scaffolding matrix material powders of anaverage size 2; and (v) producing an electrode from the mixture of thecomposite particles/powders A and B.

In some configurations, at least one of the electrodes may beinfiltrated with a solid (at room temperature) electrolyte compatiblewith the electrode in order to prevent undesirable side reactionsbetween a liquid electrolyte and the electrode active material (such asactive material dissolution during cycling or irreversible solvent orsalt decomposition, to provide a few examples of the side reactions).

FIGS. 18 and 19 illustrate example battery (e.g., Li-ion battery)building blocks, where two different electrolytes are used for the anodeand cathode, respectively, and where at least one electrolyte is solidand infiltrated into the pores between the individual particles of theelectrode. The building block example 1800 of FIG. 18 includes (i) acathode current collector 1801 coated with an electrode composed ofcathode particles 1802 and infiltrated with a suitable solid electrolyte1803, and (ii) an anode current collector 1806 coated with an electrodecomposed of anode particles 1805 and infiltrated with a suitable solidor liquid electrolyte 1804. In another example, the cathode currentcollector 1801 coated with an electrode composed of cathode particles1802 may be infiltrated with a suitable liquid electrolyte, while theanode current collector 1806 coated with an electrode composed of anodeparticles 1805 may be infiltrated with a suitable solid electrolyte1804. The building block example 1900 of FIG. 19 includes (i) a cathodecurrent collector 1901 coated with an electrode composed of cathodeparticles 1902 and infiltrated with a suitable solid electrolyte 1903,and (ii) an anode current collector 1906 coated with a metal anode layer1905 and coated with a suitable solid electrolyte 1904. In anotherexample, the cathode current collector 1901 coated with an electrodecomposed of cathode particles 1902 may be infiltrated with a suitableliquid electrolyte, while the anode current collector 1906 coated with ametal anode layer 1905 may be coated with a separator membraneinfiltrated with a suitable liquid electrolyte 1904.

Good compatibility between the active material and a solid electrolytemay be helpful in preventing damage to the active material and achievingfavorable performance at an electrode- or cell-level over a broadtemperature range of cell operation and the broad range of potentials ofelectrode operation. In one suitable example, a halide-based conversioncathode (for example, a fluoride-based cathode) may be melt-infiltrated(or, vapor infiltrated) with a halide-based (or oxy-halide based) solidelectrolyte. The composition of the halide electrolyte may be selectedto exhibit a melting point from around 100° C. to around 600° C. (forexample, by selecting a eutectic composition of such an electrolyte).The solid electrolytes may also be preferably selected to exhibitsufficiently high Li-ion conductivity (e.g., greater than 0.005 mS/cm)in the temperature range from around 0° C. to around 100° C.). Inanother suitable example, a halide-based conversion cathode (forexample, a fluoride-based cathode) may be melt-infiltrated (or vaporinfiltrated) with a nitrate-based solid electrolyte. The composition ofthe nitrate electrolyte may be selected to exhibit a melting point fromaround 100° C. to around 500° C. Similarly, the solid electrolytes mayalso be preferably selected to exhibit sufficiently high Li-ionconductivity (e.g., greater than 0.005 mS/cm) in the temperature rangefrom around 0° C. to around 100° C.). In yet another example, asulfide-based conversion cathode may be infiltrated with a sulfide-basedsolid electrode. Such an infiltration may also take place through aseries of vapor and liquid infiltration steps and may be followed by anelectrode annealing at a temperature from around 80° C. to around 600°C., depending on the electrolyte composition. In yet another example, ahigh voltage intercalation-type cathode (e.g., a cathode with an averageworking potential in the range from around 3.9 to around 5.5 V vs.Li/Li′) that exhibits a specific capacity in the range from around 140to around 340 mAh/g may be melt-infiltrated with a halide-based (oroxy-halide based) solid electrolyte having a melting point from around100° C. to around 600° C. The solid electrolytes may preferably beselected to exhibit sufficiently high Li-ion conductivity (e.g., greaterthan 0.005 mS/cm) in the temperature range from around 0° C. to around100° C.

While some of the above-discussed electrolytes may have been previouslyinvestigated (e.g., for Li, Li-ion, F-ion, Cl-ion and other types ofbatteries), their combination with the above-discussed high-energycathode materials and implementation of the melt-infiltration orvapor-infiltration steps provides substantial improvements in cellstability and energy density. Furthermore, the present disclosureprovides for overcoming the inherent limitations of many cellscomprising such electrolytes and low potential (e.g., 0-1.5 V vs.Li/Li+) anodes by utilizing a suitable liquid or a suitable solidelectrolyte for the anode side of the cell.

Selection of suitable liquid electrolytes for use in the anodes (incombination with cathodes infiltrated with solid electrolyte) depends onthe relevant anode and solid electrolyte chemistry. The followingprovides illustrative examples of the classes of solvents that may be apart of suitable liquid electrolytes that work well for many Li-ion,Na-ion, rechargeable Li and rechargeable Na batteries (in combinationwith solid-electrolyte-infiltrated cathodes): (i) esters, (ii) sulfones,(iii) sulfoxides, (iv) nitriles, (v) phosphorous-based solvents, (vi)silicon-based solvents, (vii) ether-based solvents, and (viii)carbonate-based solvents. Esters, ether-based solvents, andcarbonate-based solvents may be particularly attractive for electrolytesused for low-potential (0-1.5 V vs. Li/Li+) anodes. Illustrativeexamples of such anodes may include anodes comprising Si, Al, Sn, andother alloying-type anode materials, C (e.g., graphite) and Li (e.g., asLi or Li alloy), to name a few. Solvents comprising ethers orether-based compounds may be particularly attractive for battery cellswith Li-comprising anodes. Illustrative examples of salts that may be apart of the suitable liquid electrolyte for Li-ion, Na-ion, rechargeableLi and rechargeable Na batteries (in combination withsolid-electrolyte-infiltrated cathodes) may include: LiPF₆, LiBF₄,LiClO₄, lithium imides (e.g., CF₃SO₂N (Li+)SO₂CF₃, CF₃CF₂SO₂N(Li+)SO₂CF₃, CF₃CF₂SO₂N (Li+)SO₂CF₂CF₃, CF₃SO₂N (Li+)SO₂CF₂OCF₃,CF₃OCF₂SO₂N (Li+)SO₂CF₂OCF₃, C₆F₅SO₂N (Li+)SO₂CF₃, C₆F₅SO₂N (Li+)SO₂C₆F₅or CF₃SO₂N (Li+)SO₂PhCF₃, and others), lithium halides (e.g., LiF, LiI,LiCl, LiBr), other lithium phosphates (e.g., lithiumtris[1,2-benzenediolato(2-)-O,O′ ]phosphate, lithiumtris[3-fluoro-1,2,2-benzenediolato(2-)-O,O′] phosphate, lithiumtris(oxalate)phosphate, lithium tetrafluorooxalato phosphate, etc.),other lithium borates (e.g., lithium perfluoroethyl trifluoroborate,lithium (malonatooxalato)borate, lithium bi(polyfluorodiolato)borate,lithium difluoro(oxalate)borate, lithium tetracyanoborate, dilithiumdodecafluoro dodecarborate, etc.), lithium aluminates (e.g., lithiumtetra(1,1,1,3,3,3-hexafluoro-iso-propyl) aluminate, lithiumtetra(1,1,1,3,3,3-hexafluoro-2-butyl) aluminate, lithiumtetra(1,1,1,3,3,3-hexafluoro-2-propylphenyl) aluminate, lithiumtetra(perfluorobutyl) aluminate, etc.) and their combinations, to name afew suitable Li salts (as well as analogous Na salts). Salts comprisingLiPF₆, LiBF₄, LiClO₄, lithium imides or lithium halides may beparticularly attractive for the battery cells with Li-comprising anodes(as well as analogous Na salts for Na-comprising anodes). Inconventional Li-ion or rechargeable Li batteries only Li-based salts areutilized (mostly LiPF₆). However, a mixture of Li and non-Li salts(e.g., (i) salts of rare earth elements, such as La, Y, Sc, Ce, etc.,(ii) salts of some of the suitable alkaline metals, such as Mg, Ca, Sr,Cs, Ba, and (iii) salts of some of the suitable transition metals, suchas Zr, Hf, Ta, Cu) may be advantageous for some aspects of the presentdisclosure. The same may also apply for the Na-ion or rechargeable Nabatteries. In conventional Li-ion, Na-ion or rechargeable Li or Nabatteries, the liquid electrolyte salt concentration typically rangesfrom around 0.8M to around 1.2M. However, a higher salt concentration(e.g., from approximately 1.5M to approximately 6M) may be advantageousfor some aspects of the present disclosure.

In some configurations, a polymer electrolyte may be used instead of theliquid electrolyte for low-potential (0-1.5 V vs. Li/Li+) anodes (e.g.,anodes comprising Si, Al, Sn, or other alloying-type anode materials, C(e.g., graphite) or Li (e.g. Li or Li alloy), etc.). In someconfigurations, the polymer electrolyte infiltration may proceed in aliquid phase.

Selection of suitable liquid electrolytes for use in the cathodes (incombination with anodes infiltrated with a solid electrolyte or coatedwith a solid electrolyte) depends on the relevant anode, cathode, andsolid electrolyte chemistry. The following provide illustrative examplesof the classes of solvents that may be a part of suitable liquidelectrolytes that work well for many Li-ion, Na-ion, rechargeable Li andrechargeable Na batteries (in combination withsolid-electrolyte-infiltrated anodes or solid-electrolyte-coatedanodes): (i) esters, (ii) sulfones, (iii) sulfoxides, (iv) nitriles, (v)phosphorous-based solvents, (vi) silicon-based solvents, (vii)ether-based solvents, (viii) carbonate-based solvents, (ix) fluorinatedanalogs of these solvents, and their combinations. Esters, ether-basedsolvents, and carbonate-based solvents may work well for electrolytesused with a moderate potential (1.5-4.0 V vs. Li/Li+) cathodes (e.g.,fluoride-based or sulfide-based cathodes). Nitriles and some of thefluorinated solvents may work particularly well for electrolytes usedwith a high potential (4.0-5.5 V vs. Li/Li+) cathodes (e.g., polyanionbased cathodes). Illustrative examples of salts that may be a part ofthe suitable liquid electrolyte for Li-ion, Na-ion, rechargeable Li andrechargeable Na batteries (in combination withsolid-electrolyte-infiltrated or solid electrolyte-coated anodes) mayinclude: LiPF₆, LiBF₄, LiClO₄, lithium imides (e.g., CF₃SO₂N(Li+)SO₂CF₃, CF₃CF₂SO₂N (Li+)SO₂CF₃, CF₃CF₂SO₂N (Li+)SO₂CF₂CF₃, CF₃SO₂N(Li+)SO₂CF₂OCF₃, CF₃OCF₂SO₂N (Li+)SO₂CF₂OCF₃, C₆F₅SO₂N (Li+)SO₂CF₃,C₆F₅SO₂N (Li+)SO₂C₆F₅ or CF₃SO₂N (Li+)SO₂PhCF₃, and others), lithiumhalides (e.g., LiF, LiI, LiCl, LiBr), other lithium phosphates (e.g.,lithium tris[1,2-benzenediolato(2-)-O,O′]phosphate, lithiumtris[3-fluoro-1,2,2-benzenediolato(2-)-O,O′] phosphate, lithiumtris(oxalate)phosphate, lithium tetrafluorooxalato phosphate, etc.),other lithium borates (e.g., lithium perfluoroethyl trifluoroborate,lithium (malonatooxalato)borate, lithium bi(polyfluorodiolato)borate,lithium difluoro(oxalate)borate, lithium tetracyanoborate, dilithiumdodecafluoro dodecarborate, etc.), lithium aluminates (e.g., lithiumtetra(1,1,1,3,3,3-hexafluoro-iso-propyl) aluminate, lithiumtetra(1,1,1,3,3,3-hexafluoro-2-butyl) aluminate, lithiumtetra(1,1,1,3,3,3-hexafluoro-2-propylphenyl) aluminate, lithiumtetra(perfluorobutyl) aluminate, etc.) and their combinations, to name afew suitable Li salts (as well as analogous Na salts). Salts comprisingLiPF₆, LiBF₄ or lithium imides may be particularly attractive forbattery cells comprising high voltage (4-5.5 V vs. Li/Li+) cathodes (aswell as analogous Na salts for Na-ion and rechargeable Na batteries). Inconventional Li-ion or rechargeable Li batteries, only Li-based saltsare utilized (mostly LiPF₆). However, a mixture of Li and non-Li salts(e.g., (i) salts of rare earth elements, such as La, Y, Sc, Ce, etc.,(ii) salts of some of the suitable alkaline metals, such as Mg, Ca, Sr,Cs, Ba, and (iii) salts of some of the suitable transition metals, suchas Zr, Hf, Ta, Cu) may be advantageous for some aspects of the presentdisclosure. The same may also apply for the Na-ion or rechargeable Nabatteries. In conventional Li-ion, Na-ion or rechargeable Li or Nabatteries, the liquid electrolyte salt concentration typically rangesfrom around 0.8M to around 1.2M. However, a higher salt concentration(e.g., from approximately 1.5M to approximately 6M) may be advantageousfor some aspects of the present disclosure.

In some configurations, one of the electrodes may be infiltrated(filled) with a solid electrolyte prior to cell assembly, while anotherelectrode is infiltrated with a second type of electrolyte (which may beeither solid or liquid) after cell stack assembly, but prior to thefinal sealing.

One consideration is the lack of unfavorable interactions between thetwo types of electrolytes. The rationale for the use of a combination ofdifferent electrolytes for anodes and cathodes may be related to theircompatibilities. For example, the use of a halide or oxyhalide (and, insome cases, nitrate, nitrite, and nitride) electrolyte may beadvantageous for conversion-type cathodes (for example, metalfluoride-based) and, in some cases (for example, in the case of manyhalide or oxyhalide electrolytes), high voltage polyanion intercalationtype cathodes (particularly those with an average Li extractionpotential in the range from around 3.9 to around 5.5 V vs. Li/Li+)because of the stability of most of the halide electrolytes in thecorresponding voltage range (for example, from around 2 to around 5.5 Vvs. Li/Li⁺). Nitrate based electrolytes are commonly stable to around4-4.5 V vs. Li/Li+.

Many halide, oxyhalide, nitrate, nitrite, nitride and other electrolytesmay be melt-infiltrated and thus offer high volumetric capacity to theelectrodes. However, some halide-based electrolytes and some polymerelectrolytes are not stable at the low potential of some of the anodes(for example, from around 0 to around 1.5 V vs. Li/Li+), which mayprohibit their direct electrical contact with such anodes in cells. Incontrast, many known liquid electrolytes and some solid (for example,polymer based and nitrate, nitrite, and nitride) electrolytes may becompatible with low potential anode materials (for example, thoseoperating in the range from around 0 to around 2 V vs. Li/Li+ duringcycling), at least after forming a so-called solid electrolyteinterphase (SEI) layer on these anodes. However, they may oxidize athigh potentials (for example, at above around 4 V vs. Li/Li+), therebyinducing gases into cells, or may induce undesirable interactions with acathode active material (e.g., dissolution of at least some portions ofsuch an active material or formation of undesirable interphase species).

In another example, a given solid electrolyte may be difficult toinfiltrate into a porous structure of an electrode without reducing itsvolumetric capacity. In some configurations, it may be preferable to usesuch an electrolyte with a flat metal anode (for example, with Li metalor a Li-comprising anode in the case of Li cells) and use anotherelectrolyte (less useful in combination with such an anode) that couldbe successfully and efficiently infiltrated into a cathode withoutreduction of the cathode volumetric capacity (for example, if such anelectrolyte may be infiltrated in a liquid state). In other examples, itis possible to effectively melt-infiltrate two solid electrolytes in theanode and cathode, respectively (for example, infiltrate a halideelectrolyte into a high voltage or conversion-type cathode and Li₃N intoan alloying-type anode). All such configurations may be particularlyuseful for rechargeable metal and metal-ion cells (such as Li-ion andrechargeable Li cells).

FIG. 20 illustrates an example metal-ion (e.g., Li-ion) battery in whichthe components, materials, methods, and other techniques describedherein, or combinations thereof, may be applied according to variousembodiments. A cylindrical battery is shown here for illustrationpurposes, but other types of arrangements, including prismatic or pouch(laminate-type) batteries, may also be used as desired. The examplebattery 2000 includes a negative anode 2002, a positive cathode 2003, aseparator 2004 interposed between the anode 2002 and the cathode 2003,an electrolyte (not shown) impregnating the separator 2004, a batterycase 2005, and a sealing member 2006 sealing the battery case 2005.

For some designs, a battery electrode composition is provided, where theelectrode changes properties (e.g., composition, mechanical properties,microstructure, density, porosity, average pore size, etc.) from thesurface of the electrode to the interface with a current collector (suchas a metal foil). In some configurations, producing a gradient at theelectrode level may be advantageously combined with a gradient inproperties at the particle level.

For some designs, the described change(s) in electrode properties may beachieved in particle-based electrodes, where, for example, differentparticles (e.g., particles of different size, different composition,different density, etc.), different amounts (or relative fraction orcomposition) of the binder, or different amounts (or relative fractionor composition) of conductive additives may be used across the electrodethickness. Such an approach may slightly complicate the electrodefabrication, but provides multiple benefits. For example, higherporosity (larger open space between the individual particles) near theelectrode surface may improve electrolyte access to the inner (deeper)electrode areas, thus enhancing electrode rate performance. Whencompared to a uniform electrode of the same density, an electrode withrationally optimized gradient properties may exhibit not only higherrate, but also longer cycle life, because electrode particles are moreequally stressed (charged-discharged) during cycling (e.g., more equallylithiated and delithiated in the case of Li-ion batteries). Overchargeor over-discharge of high capacity materials are known to induce fasterdegradation. Therefore, if some of the electrode particles (e.g., nearthe top/surface layer of the electrode) degrade, the whole cell may faderapidly. Volume changes within individual high capacity particles inexcess of around 8% may induce significant stresses at the interfacewith current collectors (e.g., Cu in the case of low potential Li-ionbattery anodes or Al in case of Li-ion battery cathodes), which mayresult in plastic deformation and fracture of the current collectors orfailure of the electrode/current collector interfaces. Therefore,providing electrodes that exhibit lower volume changes near suchinterfaces may significantly improve cell stability.

Different profiles within the electrode thickness may be produced byseveral approaches, including casting electrodes in multiple (thinner)layers (each layer may be cast from a separate slurry of the controlledcomposition) or casting using specially designed extruders that mayincorporate multiple layers (each extruded from a separate slurrycontainer). The first approach (casting a single electrode of thedesired thickness by subsequent application and drying of multiplethinner layers of electrode compositions) has an additional advantage ofreducing the slurry solvent drying time and minimizing the stresseswithin the electrode occurring during such a drying process. Reductionin the drying time may significantly reduce the cost of electrodefabrication. As a result, thicker electrodes (with variable compositionacross their thicknesses) may exhibit better properties and, at the sametime, be produced at a reduced cost.

For some designs, the above-discussed change(s) in electrode propertiesacross the electrode thickness (such as density, porosity, composition,etc.) may be achieved in an electrode that is not based onpolymer-bonded individual particles, but is monolithic. In this case, itcan be considered to be a single large sheet-shaped composite particle.

The forgoing description is provided to enable any person skilled in theart to make or use embodiments of the present invention. It will beappreciated, however, that the present invention is not limited to theparticular formulations, process steps, and materials disclosed herein,as various modifications to these embodiments will be readily apparentto those skilled in the art. That is, the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention.

The invention claimed is:
 1. A Li-ion battery anode composition,comprising a composite particle comprising a core and an innermost shelllayer of the composite particle that at least partially encases thecore, wherein the core includes a first region from the center to afirst radius that is halfway to the innermost shell layer of thecomposite particle and a second region from the center to a secondradius at the innermost shell layer of the composite particle, whereinthe core exhibits an average material property that is different in thefirst and second regions and that changes from the center of thecomposite particle to the innermost shell layer, wherein the compositeparticle comprises an active material capable of storing and releasingLi ions during battery operation, wherein the active material exhibits aspecific capacity of at least about 400 mAh/g, wherein the corecomprises an electrically conductive matrix material, and wherein theelectrically conductive matrix material comprises carbon (C).
 2. ALi-ion battery anode composition, comprising: a composite particlecomprising a core and an innermost shell layer of the composite particlethat at least partially encases the core, wherein the core includes afirst region from the center to a first radius that is halfway to theinnermost shell layer of the composite particle and a second region fromthe center to a second radius at the innermost shell layer of thecomposite particle, wherein the core exhibits an average materialproperty that is different in the first and second regions and thatchanges from the center of the composite particle to the innermost shelllayer, wherein the composite particle comprises an active materialcapable of storing and releasing Li ions during battery operation, andwherein the active material exhibits a specific capacity of at leastabout 400 mAh/g; and at least one additional composite particle, whereinthe core comprises a matrix material that is capable of electricallyconnecting the composite particle to the at least one additionalcomposite particle.
 3. The Li-ion battery anode composition of claim 2,wherein the matrix material of the composite particle is in the form ofa unibody or a single solid particle.
 4. The Li-ion battery anodecomposition of claim 2, wherein the matrix material exhibits electricalconductivity in excess of about 10⁻² S/m.
 5. The Li-ion battery anodecomposition of claim 2, wherein Li-ion diffusion within the matrixmaterial exceeds about 10⁻⁹ cm²/s.
 6. The Li-ion battery anodecomposition of claim 1, wherein the active material exhibits a meltingpoint above about 250° C.
 7. The Li-ion battery anode composition ofclaim 6, wherein the active material comprises silicon (Si) or a Sialloy.
 8. The Li-ion battery anode composition of claim 1, wherein thecore of the composite particle comprises silicon (Si) or a Si alloy. 9.The Li-ion battery anode composition of claim 2, wherein the compositeparticle additionally comprises carbon (C).
 10. A Li-ion battery anodecomposition, comprising: a composite particle comprising a core and aninnermost shell layer of the composite particle that at least partiallyencases the core, wherein the core includes a first region from thecenter to a first radius that is halfway to the innermost shell layer ofthe composite particle and a second region from the center to a secondradius at the innermost shell layer of the composite particle, whereinthe core exhibits an average material property that is different in thefirst and second regions and that changes from the center of thecomposite particle to the innermost shell layer, wherein the compositeparticle comprises an active material capable of storing and releasingLi ions during battery operation, wherein the active material exhibits aspecific capacity of at least about 400 mAh/g, and wherein the corecomprises pores that are capable of at least partially accommodatingvolume expansion of the active material while storing one or more of theLi ions.
 11. The Li-ion battery anode composition of claim 10, whereinat least one of the pores is closed and capable of remaininginaccessible to electrolyte during battery operation.
 12. The Li-ionbattery anode composition of claim 10, wherein the average materialproperty comprises an orientation of the pores.
 13. The Li-ion batteryanode composition of claim 10, wherein the pores are capable ofaccommodating between about 20% to about 100% of the volume expansion ofthe active material while storing one or more of the Li ions.
 14. TheLi-ion battery anode composition of claim 13, wherein the pores arecapable of accommodating less than about 100% of the volume expansion ofthe active material while storing one or more of the Li ions, andwherein the composite particle is capable of resisting fracture, viaplastic or elastic deformation, in response to force from residualvolume expansion of the active material that is not accommodated by thepores.
 15. The Li-ion battery anode composition of claim 1, wherein aweight fraction of the active material in the composite particle is fromaround 20% to around 99 wt. %.
 16. The Li-ion battery anode compositionof claim 1, wherein the average material property comprises anorientation of a weight fraction of the active material, and wherein thecore comprises a higher weight fraction of the active material in thefirst region compared to the second region.
 17. The Li-ion battery anodecomposition of claim 1, wherein the average material property comprisesa density of the core, and wherein the core exhibits a lower density inthe first region compared to the second region.
 18. The Li-ion batteryanode composition of claim 1, wherein the average material propertycomprises a degree of disorder in the electrically conductive matrixmaterial, and wherein the core exhibits a higher degree of disorder inthe first region compared to the second region.
 19. The Li-ion batteryanode composition of claim 1, wherein the innermost shell layer is aprotective shell layer that comprises a shell material that issubstantially impermeable to an electrolyte solvent while remainingpermeable to the Li ions.
 20. The Li-ion battery anode composition ofclaim 1, wherein the innermost shell layer is the only shell layer ofthe composite particle.
 21. The Li-ion battery anode composition ofclaim 1, wherein the innermost shell layer is one of a plurality ofshell layers of the composite particle, each of the plurality of shelllayers having a different composition.
 22. The Li-ion battery anodecomposition of claim 1, wherein at least part of the innermost shelllayer is in direct contact with the core.